From about 4000 BC, a loose network of nomadic tribes from Southern Russia began to spread out in separate groups over the Eurasian continent. Their spread accelerated around 2000 BC, with the invention of the swift horse-powered war chariot with spoked wheels, which turned these nomadic herders into powerful warriors. They spread out over an area all the way from Western Europe to the borders of China, crushing many unexpected enemies along their way. The shared language of these warriors is called Indo-European, which has become the basis for most languages in this vast area, including English, Germanic, Greek, Italian, Persian, and Sanskrit (Indian). Although the original Indo-Europeans were illiterate, linguists have managed to reconstruct many of the words they used by comparing the languages in this vast area. These words, in turn, give us insights into their habits and even their mythology.
In the 18th century, a British judge in India named William Jones noticed similarities between English, Latin, Greek, and the Indian language named Sanskrit. He concluded that these languages have “a stronger affinity, both in the roots of verbs and in the forms of grammar, than could possibly have been produced by accident; so strong indeed, that no philologer could examine them all three without believing them to have sprung from some common source, which, perhaps, no longer exists.”  Over the years, we have found these similarities in many more languages, located in the area ranging from Europe to the edge of China. This includes most of the languages of Europe (except for Basque, Finnish, Estonian, and Hungarian), the Persian languages of Iran, Sanskrit and its many modern daughter languages (including Hindi and Urdu), and a number of extinct languages, including Hittite (from Turkey) and Tocharian (from the deserts of northwestern China). Take, for instance, the Sanskrit word “agni,” meaning “fire,” which is still related to the English word “ignite.” The Sanskrit word “atman,” meaning “to breathe,” is related to the German word “atmen,” which has the same meaning.
Fig. 210 – The Indo-European language tree. (EnriBrahimaj, CC BY-SA 4.0)
We now call the common source of these languages Proto-Indo-European (PIE). Unfortunately, this language died out around 2500 BC, and since the people who spoke it were illiterate, not a single word of this language has come down to us directly. Yet, by comparing its daughter languages, linguists have managed to reconstruct about 1500 of its words with reasonable certainty.
How did they do this? First of all, there are regularities in the ways spoken words change over time. For instance, all words in Latin starting with “ke-” transformed in Medieval French into “tse-,” and in French into “se-,” making these words progressively easier to pronounce. Take for instance the Latin word “kentum,” meaning “hundred,” which first became “tsentm” and later “cent.” These changes were specific to “ke-” words and did not occur, for instance, to words starting with “ko-” (for instance, the Latin “costa” became the French “cote”). These changes are generally so predictable that they allow linguists to backtrack the previous incarnation of a word. 
Linguists generally only accept a reconstructed word if it can be traced back through these well-established sound changes. Simply noticing similarities between words is not enough, as this can be due to chance. For instance, the Latin word “deus,” meaning “god,” does not share a common root with the Greek word “theos,” also meaning “god.” Also, the Greek sky-god Ouranos and the Indian sky-god Varuna show similarities both in their names and their mythological aspects, yet we have not managed to derive their names back to a common root. In both cases, it is still possible these words stem from a common root in some irregular way, but this cannot be proven.
With this toolkit, the word “hundred,” for instance, was traced back to the PIE-root “kmtom,” which in Proto-Germanic became “kumtom,” then “humdan,” and then “hunda”, which finally evolved into the English word “hundred.” The PIE-root “kmtom” also became “catam” in Proto-Indo-Iranian, “satem” in Avestan (Old Iranian), and “sata” in Sanskrit. Comparing all these languages, the PIE-root “kmtom” turned out to be the only word that can develop in all its daughter words through established sound changes.
The validity of these techniques has since been tested empirically several times. In three cases so far, a reconstructed word was later discovered to actually exist. For instance, the PIE-root “ghosti,” meaning “guest,” was predicted to become “gastiz” in Proto-Germanic. This word was later discovered in Denmark. Similarly, the Proto-Greek sound “kw” was first completely theoretical, but was later discovered on early Greek Linear B tablets.
Linguists have also looked at the rate at which languages change over time. Roughly, and with some exceptions, it takes about a thousand years for a language to become incomprehensible to its original speakers. From this observation, we can roughly calculate how long ago two languages diverged from their common ancestor. Let’s see where this method brings us. The oldest language known to detach from PIE was Proto-Anatolian, the now-extinct precursor to the language written by the Hittites in Turkey. We know this language must be the oldest Indo-European branch, since Hittite contains a lot of archaic elements we do not see in the other Indo-European languages. Hittite is also the oldest Indo-European language we have in writing. The first isolated words are dated to about 1900 BC, while the first text (the Anitta Text) is dated to the 17th century BC. By comparing Hittite with related languages, it is estimated that Proto-Anatolian must have existed around 3400 BC and must have split from PIE around 4000 BC.
Interestingly, Hittite is also the only Indo-European language that does not contain a clear PIE-root for “wheel” or other words related to wagons, making it likely that Anatolian split before the invention of the wheel around 3500 BC. The PIE-root for wheel became “kweklos,” derived from the word “kwel,” meaning “to turn.” The proto-Indo-Europeans also had related words, such as “axle,” “wagon,” and a verb meaning “to enter a vehicle.” 
Proto-Italic and Proto-Celtic likely split from PIE before 2500 BC. Proto-Greek formed after 2500 BC and morphed into Greek around 1650 BC (the oldest Greek Linear B tablets date to 1450 BC). Proto-Indo-Iranian, which later developed into the Persian and Indian languages, appeared around 2000 BC. The oldest texts written in Sanskrit date to around 1500 BC. This includes the Rig Veda, from India, but curiously also some texts from the Mitanni Empire, all the way in northern Syria. The Mitanni commoners spoke a non-Indo-European language named Hurrian, but the kings took Sanskrit names. For instance, the royal name Tusratta (Tvesa-ratha) is Sanskrit for “having an attacking chariot.” The name Artatama (Rta-dhaaman) contains the word “rta,” which became an important concept in India, meaning “cosmic order.” The Mitanni capital, Wassukanni (vasu-khani), is Sanskrit for “wealth mine.” In a treaty with the Hittites from around 1380 BC, the Mitanni king named Kurtiwaza even explicitly named Indian gods from the Rig Veda, including Indra, Varuna, Mithra, and the Nasatyas. Like many Indo-European people, the Mitanni were great charioteers. They even wrote the earliest known horse-training manual, written around 1350 BC by a man called Kikkuli. 
The earliest extant text from the Persian branch is the Avesta, associated with the prophet Zarathustra (Zoroaster in Greek). The oldest parts, known as the Gathas, are dated by linguists between 1200 and 1000 BC. As we will later read in more detail, these texts also contain the names of various Indian gods from the Rig Veda.
Thus far, we have reconstructed the Indo-European language tree, but we have yet to discover where the Proto-Indo-Europeans lived. Through great detective work, linguists have traced this place back to the steppes just north of the Black and Caspian Seas in what is today southern Ukraine and Russia. How do we know this? The trick is by looking at the PIE vocabulary. We can learn a lot about a people simply by learning what words they speak, which can then be matched against the archeological record. A great start is to look at words for animals and plants. The PIE vocabulary does not include the names of Mediterranean or tropical species, which rules out these areas. They did have a word for “horse” (“ekwo”), which at the time only lived in the steppes of Eurasia. We also have words for “honey” and “bee,” which rules out Siberia and the Central Asian steppes. The presence of words for domesticated animals, including “cow,” “ox,” “sheep,” and “pig,” rules out places occupied solely by hunter-gatherers. Since there is no word for “city” in PIE, we also expect them to be nomads. Finally, we can search for words which the Proto-Indo-Europeans borrowed from their neighbors. These words come mainly from Proto-Uralic, from the southern flanks of the Ural Mountains. All these clues together point to the steppes just north of the Black and Caspian Sea. 
Archeological research in this area further strengthened this conclusion. Evidence suggests that people migrated out of this area in separate groups in a number of waves. These waves roughly correspond both in time and direction with the spread of Indo-European languages as described above.
In hunter-gatherer days, the grassland of the steppes was an unfriendly environment for human beings. This changed with the domestication of sheep and cattle, since these animals can turn grass into useful products, such as meat, milk, and wool. The domestication of the horse also was of great use. Because of its speed, it allowed nomads to have a larger herd and spread out over a much larger territory. Evidence seems to suggest that the first horse riders appeared around 3500 BC, since at this time the teeth of horses began to show bit wear. The earliest evidence for horse-drawn chariots with spoked wheels comes from about 2000 BC, from the Sintashta culture, just northeast of the PIE homeland. With spoked wheels, chariots were much faster than wagons with heavy solid wheels. 
The Sintashta people created a number of fortified settlements and elaborate burial sites. Their main settlement, also called Sintashta, was a fortified circular town of about 140 meters in diameter, surrounded by an earthen wall reinforced with wood, complete with a number of wooden towers. Inside, archeologists have found the ruins of 31 houses, each containing hearths and copper remains, suggesting Sintashta was a metallurgical industrial center. Just outside the town, a number of spectacular burials were found, which include the remains of horses, bronze and copper weapons, silver and gold ornaments, and, most importantly, the oldest chariots ever found (see Fig. 211). Up until this point, 16 chariots have been found associated with the Sintashta culture.
Fig. 211 – Sintashta Grave 30 containing one of the oldest chariots ever found. The wooden spoked wheels have rotten, but left stains in the earth. On the right, we see cheekpieces for horses, which were used to attach bits (S. P. Dinkgreve, worldhistorybook.com, after Gening and Zdanovich, 1992)
Interestingly, the Sintashta funeral practices show clear similarities with rituals described in the Indian Rig Veda, making it plausible that the people of Sintashta spoke Proto-Indo-Iranian, the precursor to the Indian and Persian languages. The Rig Veda describes hills containing roofed burial chambers supported with wooden posts, which closely matches the Sintashta grave pits. The Vedas also describe a horse sacrifice (ashvamedha) at a royal funeral, which included a public feast. These feasts also seem to have been part of the Sintashta culture. In one Sintashta grave we have found the heads of six horses, four cows, and two rams, which together produced 3000 kilograms of meat. Finally, the Vedas also mention that the lower limbs of the sacrificial horses should remain undamaged and placed in a pattern, something we can also see in the Sintashta graves.
The invention of the chariot was soon picked up by other cultures. In the 17th century BC, it was used by the Hyksos to invade and conquer Egypt, and around 1500 BC it was in use both in Mycenaean Greece and Shang China.
The reconstructed vocabulary of PIE also gives insight into the social organization among the Proto-Indo-Europeans. They used to live in households (“domh”) containing one or more families (“genhes”). These families were further organized into clans (“weik”), each led by a clan leader (“weik-potis”). A number of related clans formed a tribe (“heros”). We also have a word for “ruler” (“hregs”), which became “rex” in Latin and “raj” in Sanskrit. The word, in turn, is derived from “hreg,” meaning “to make straight” (which became “rectus” in Latin, “rju” in Sanskrit, and “right” in English). The rulers possessed most of the wealth of the tribe, which for nomads meant they possessed the most animals (their “movable wealth” or “peku”). Since herd animals were in such high demand, they were often stolen. This is reflected in a verb meaning “to raid or steal cattle,” which occurs in Celtic, Italic, and Sanskrit. In Sanskrit, the word “gavisthi,” originally meaning “desire for cows,” eventually became their word for “fighting.”
As nomads often find themselves in the territory of other tribes, great emphasis was placed on the importance of guest-host relationships (both the word “host” and “guest” derive from the PIE-root “ghosti”). Individuals of the tribe felt an obligation to invite foreign allies into their communities and treat them well. We see this reflected in various Indo-European cultures, especially in Greece, where the word had morphed into “xenia.” There even was a theme in Greek myth called theoxenia, where the hospitality of a human being was tested by a deity disguised as a poor man. Zeus was sometimes called Zeus Xenios, highlighting his role as protector of strangers (in the Odyssey we read “beggars come from Zeus”).
With the tools of linguistics, it is even possible to peer into the minds of the Proto-Indo-Europeans. From their vocabulary, we know they deeply valued poetry, which they did not consider to be a secular art, but a divine calling. “Calling to mind a poem,” for which they used the PIE-root “men,” was believed to literally require the gods to whisper the words to them (“men” became “manyate” in Sanskrit, is related to the Sanskrit word “mantra,” and became “to mention” in English). In Greek, bards often started their poems by asking the Muses (also from the PIE-root “men”) to assist them in calling to mind the words of a poem. This also explains why the Muses were the daughters of the goddess of memory (Mnemosyne). Similarly, Odin, the god of poetic inspiration, had two ravens called Huginn and Muninn (meaning “thought” and “recall”). 
Poems in Indo-European cultures were performed by both professional priests and divinely inspired storytellers. These poets were taken on as patrons by aristocratic families and were often richly rewarded with horses and cattle (we see this clearly among the Celts and the Indians). We will meet a number of Indo-European poets in later chapters, among them the bard Homer from Greece, who sang about the Trojan War, and the rishis of India who composed the divinely inspired hymns of the Rig Veda. We also meet them in Celtic lands. The Greek polymath Posidonius, writing in the early first century BC, reported that the Celts had bards (“bardoi”) who sang songs about the brave deeds of warriors accompanied by lyres. The word “bard” goes back to “gwrhdhho,” meaning “praisemaker,” which in turn was derived from “gwerh” meaning “to praise.” The word also ended up in Sanskrit as “gir” (“praise-song”) and “gr” (“to praise”). Through the praise of the bards, the Indo-European chieftains hoped to win fame and glory in order to be remembered by future generations. We find this idea in Greece as “kleos aphthiton” and in India as “sravas aksitam,” both meaning “unfading glory” (both derived from the PIE-root “klewos ndhgwhitom”). For the word “glory” or “fame,” the Proto-Indo-Europeans used “klewes,” which was derived from “klu,” meaning “to hear [about]”. It later appeared in Irish as “clu” and all the way in Tocharian (western China) as “klyu.” We find the sentiment of attaining eternal glory in many Indo-European tales. In Old English, we find it in the story Beowulf (“you have achieved it by your deeds that your reputation will live for evermore.”), in India it is verbalized by the hero Karna from the Mahabharata (“I choose fame on earth even at the cost of my life”), and in Ireland by Cu Chulainn (“If I can only be known by name, I am content to live but a single day.”) The best examples, however, come from the Iliad by Homer, which we will discuss in a later chapter.
Besides bards, Posidonius also recorded druids (dryidai) among the Celts, who presided over sacrifices and functioned as judges. Finally, there were the vates, who foretold the future. The word “vates” appeared in Latin as “uates,” meaning an “inspired poet” and is related to “wops” (“possessed”) in Gothic, “wuot” (“frenzied”) in Old High German, and “wod” (“song”) in Old English. This link between poetry and divine possession appears several times among the Indo-European languages. The Sanskrit word “rsi” (or “rishi,” meaning “sage”) turns out to be related to the German word “rasen,” meaning “to rage.” Similarly, the Greek word for “seer” is “mantis,” which originally meant “frenzied.” 
Mythology in the vast Indo-European terrain also shows many commonalities. Take, for instance, the god Indra in India and Zeus in Greece. Both were warrior sky gods, each the king of a pantheon of gods, and both wielded the thunderbolt as their weapon (see Fig. 212 and Fig. 213).
Fig. 212 – Zeus fighting Porphyrion with his thunderbolt (c. 400 BC) (ArchaiOptix, CC BY-SA 4.0; Staatliche Museen zu Berlin)
Fig. 213 – Indra wielding the thunderbolt (10th century) (Photo Dharma, CC BY-SA 2.0; Banteay Srei Temple, Cambodia)
Linguists have even derived the names of a number of Proto-Indo-European gods. Their main god seems to have been a sky god. His name was related to “dyu,” meaning “bright sky” or “the light of day,” which in Latin became “dies,” in Sanskrit “dive,” and in English “day.” The name of the sky god was “Dyeus,” which in Sanskrit became “Dyaus,” and in Greece became “Zeus.” As the father of the gods, the sky god also became known in Sanskrit as “Diaus pitar,” in Greek “Zeus pater,” and in Latin it was shortened to “Jupiter” (from “Dies piter”). The related word “deiwos” became a word for “god,” which in Sanskrit became “deva,” in Avestan “daeva,” in Latin “deus,” and in Hittite “sius” (the Greek word “theos” is unrelated, going back to “dhesos,” which is derived from “dheh,” meaning “to do” or “to place”). The English word “god” is derived from “ghutos,” referring to a liquid poured out as an offering to the gods. The word is also related to the Dutch word “gieten” and the Sanskrit “hu,” both meaning “to pour”. 
While the gods were associated with the sky, human beings were made from the earth, for which the PIE-root is “dheghom.” This word became “humus” in Latin, which is related to “homo,” meaning “man.” In Greek, the word for “earth” became “khton,” and in Sanskrit “ksam.” In many Indo-European cultures, the Earth became personified as Mother Earth (“dheghom mehter”), although the linguistic connection is not as strong as with Father Sky. For instance, the name of Mother Earth in the Rig Veda was Prithvi (or Prithvi Mata), while in Greece she got the unrelated names Gaia and Ge. There is a possibility that the name of the Greek goddess of wheat, Demeter, was derived from “Damater,” with “da” derived from “dhghem” (earth) and “mater” meaning “mother.”
In many Indo-European cultures, Father Sky and Mother Earth became the parents of the gods. In Greece, the role of Father Sky somehow switched from Zeus to Ouranos, while Zeus became a storm god and the king of the gods.
Father Sky also had a daughter, called the Sky Daughter (“dhughter diwos”), who was the goddess of dawn (“hewsos”). In Sanskrit, she is called Usas, in Greek Eos, and in Latin Aurora, all from the PIE-root “hues,” meaning “(red) glow.” The sky god also had divine twins, which in various cultures became associated with horse riding and the chariot. In the Rig Veda, these twins were called the Asvins or the Nasatya. In Greece, they were known as the Dioskouroi. In both cases, these gods were known to rescue humans from danger.
There also seems to have been a Proto-Indo-European sun god, who is often described as a surveyor of the world, and therefore associated with justice. The disk of the sun is often described as being drawn by a horse. We find this symbolism in Greece, in India, and also in Scandinavia (see Fig. 214).
Fig. 214 – The Trundholm Sun Chariot (c. 1400 BC) (National Museum of Denmark, CC BY-SA 3.0)
The Proto-Indo-European sun god also had a daughter. In India, she was called Surya and she joins the Ashvins in their chariot, who are described as her husbands. In Greece, the Dioskouroi are related to Helen, who here isn’t the daughter of the sun, but of Zeus, and who is not their wife, but their sister. In the story of the Trojan War, Helen was a mortal woman, but in some places she was worshipped as a goddess. According to one theory, her connection to the sun comes in when we note that an earlier form of her name must have been “swelena,” from the PIE-root “swel,” meaning sun. 
It is also likely there was a Proto-Indo-European storm god. Among the Celts, the storm god was Taranis, in Old High German it became Donar or Thunar, and in Old Norse it became Thor. These words seem related to the Latin word “tonare” and the Sanskrit word “tan,” meaning “thunder,” although there were no thunder gods in these cultures with a related name. Some scholars believe the name of the Hittite god Tarhunna is also related.
In the Baltic area, the god of thunder was Perkunas. A possible PIE-root for this god is “perkwunos,” which is related to “perkwus” (“oak”) and “per” (“to strike”). The association of the thunder god with the oak tree is common, possibly since oaks are large trees and therefore are often hit by lightning. The name “Perkunas” might also be related to keraunos, the name for Zeus’s thunderbolt. There were also attempts to relate the name to the Sanskrit thunder god Parjanya, but this has been unsuccessful.
The Indo-European thunder gods are also described remarkably similar. Indra, the Indian storm god, is described as having a fiery or reddish beard, from which he shakes spilled liquid, which comes down as rain. Thor has links to the oak tree and also has a red beard, which he shakes when he gets angry. The word used for shake in this context, “dyja,” even corresponds to “dhu” used for Indra. Perkunas, too, is described as having a red beard. On top of this, Zeus, Perkunas, and Thor are also all described as riding a cart drawn by goats.
There might even be a PIE-root for Prometheus, the Greek god who stole fire from heaven and gave it to mankind. In Sanskrit, “pramath” means “to steal.” This verb was used to describe the theft of fire from heaven by the Indian hero Matarisvan. This character is closely related to Manu (meaning “man”), the Indian Noah who survived the Great Flood and repopulated the Earth. Similarly, Prometheus was the father of Deucalion, who also became a survivor of the Flood. Both Manu and Prometheus were also believed to have taught humanity how to sacrifice to the gods.
There also was a mysterious figure called Twin in various Indo-European mythologies. Take, for instance, the Old Norse character Ymir. He was a primal being who created the first humans and was then killed by Odin, who then molded the world from his body parts. His name means “twin,” perhaps because he was able to create human beings by himself. In Germanic mythology, we have Tuisto, who became the father of Mannus (also related to “man”), who became the ancestor of all Germans. Then there was the Sanskrit Yama (and the Avestan Yima), the Indian god of death, whose names also mean “twin”. Yama was the brother of Manu and forsook his immortality in exchange for having progeny. Some scholars also believe that Remus, the founder of Rome, and twin brother of Romulus, was originally called “Yemos,” meaning “twin.” His death at the hands of his brother was essential for the foundation of Rome. 
The PIE gods were generally not very concerned with ethics, although there were a number of gods charged with the supervision of justice. For instance, the Sanskrit god Aryaman (Airyaman in Avestan) was the god of justice, social customs, and marital oaths. He is sometimes linguistically equated with the legendary Irish king Eremon. These names are related to the Sanskrit “arya” and the Irish “aire,” both meaning “noble.” The Sanskrit gods Mitra (Mithra in Avestan) and Varuna were also associated with justice. They were seen as all-knowing observers of the world and therefore the perfect candidates to decide right from wrong.
The idea of spinster goddesses who decide the fate of individual human beings is found all over Europe and also among the Hittites. There were no spinster-fate goddesses in India, yet there too, human life was sometimes conceived as a thread. In Greece, there are three spinster goddesses called the Moirai. In Nordic mythology, they are called the Norns. In Old English, the power that weaves destiny is called “wyrd.” Destiny, it was said, was “woven on Wyrd’s loom.” The word is related to the German “werden” (“to become”) and “wirtel” (“spindle”), to the Latin “uertere” (“to turn”), and to the Sanskrit “vartate” (“to turn” or “to turn out”) and to “vartana” (“spindle”). Later, “wyrd” was also personified, for instance as the Werdys in Chaucer and as the Weird Sisters in Shakespeare’s Macbeth.
The concept of an underworld also had a PIE origin. From the PIE-root “hregwos,” meaning “darkness,” we get “erebos,” a Greek name for the underworld. The Latin “inferus” is related to the PIE-root “hndheros,” which in turn is derived from “hndher,” meaning “under.” The Germanic word “hell” is related to the PIE-root “kel,” meaning “to cover,” and to the Latin word “celare” (“to hide”). In various Indo-European traditions, the entrance to the underworld is guarded by a dog, often with multiple heads or eyes. In Greece, this animal was called Cerberus, from “kerberos,” meaning spotted. In India, Yama also had two dogs guarding the underworld. In various Indo-European mythologies, dead humans also crossed a river to reach the underworld.
The word for “honey” or “honey wine” (“medhu”) is also widespread. It appears in Sanskrit as “medhu,” in Tocharian as “mit,” in Greece as “methy” (wine), and in English as “mead.” In the Rig Veda, honey wine was also equated with soma (haoma in Avestan), an intoxicating drink with the power to make its consumer feel immortal. Soma was both drunk by priests and offered in a sacred fire as food for the gods. In Norse mythology, “mead of poetry” was a drink that gave poetic inspiration.
There also seems to have been a PIE myth about a hero slaying a serpent, often with multiple heads. The PIE-root was “hegwhent hogwhim” (“he killed the serpent,” with “hogwhis” meaning serpent), which in Avestan became “janat azim” and in Sanskrit “ahann ahim.” With a substituted verb, it became “kteine hophin” in Greek and with a new noun, it became “illuyanka kwenta” among the Hittites. 
Finally, we will discuss the Iranian prophet Zarathustra, whose teachings are written in a text known as the Avesta. The earliest parts of this work are called the Gathas and are written in a language known as Old Avestan, dated by linguists between 1200 and 1000 BC. The later parts of the text, written in Young Avestan, were likely written between 900 and 500 BC. In these newer parts, Zarathustra is presented as a larger-than-life mythological figure. We read of an afterlife with rewards in heaven and punishments in hell, and a physical resurrection of the dead. In the older chapters, however, he appears far more human. Here, we read about his relationships with his patrons (especially King Vishtaspa), we hear him complain that his competitors have more cows, and we hear his doubts after his message got rejected.
In the Gathas, Zarathustra is described as in competition with other poet-sacrificers, whom he rejects as false prophets. Interestingly, he used the word “kawi” for the bad poet-prophets, which in Sanskrit (“kavi”) came to have a positive connotation (it is related to the PIE-root “skeu,” meaning “to see,” and to the English word “to show”). We see this reversal of terms also in the Avestan and Sanskrit words for “gods” and “demons.” For the Zoroastrians, gods were called “ahura,” while the demons were called “daeva.” In India, this is the other way around. Here the gods are called “deva,” and the demons are called “asura” (although the oldest hymns of the Rig Veda also mention good asuras and even the important gods Indra and Agni are called asuras at this early stage). Quite shockingly, the Young Avesta even explicitly names various important Indian gods among the demons, including Indra and the Nasatyas. This swap in names might reflect an early conflict between the Indian and Avestan clans.
So what did Zarathustra believe? He imagined a world in which two forces, Order (asha) and Deceit (druj), were constantly in conflict. The god responsible for order was Ahura Mazda (meaning “lord wisdom”). In the Gathas, we read:
Ahura Mazda engendered Order, established the road of the sun and of the stars, started the phases of the moon, held the earth down below and the heavens above, established the water and the plants […] established light and darkness, sleep and wakefulness, […] dawn, noon, and evening. […] Ahura Mazda fashioned the milk-giving cow, which makes happiness.” 
The god responsible for deceit was Angra Mainyu (meaning “evil spirit”), who used chaos and falsehood to push people away from Ahura Mazda. To aid Ahura Mazda in his fight, Zarathustra taught humanity how to perform a sacrifice. According to the Young Avesta, this involved pouring the intoxicating drink haoma on a sacred fire.
Zarathustra also worried about the mistreatment of cows by his competitors (although we do read of animal sacrifice in the Young Avesta). In the Gathas, he even described the pain of a cow from the perspective of the animal. We find the cow in despair, longing for the protection of an adequate herdsman. When Zarathustra tried to alleviate her condition, the cow was at first skeptical, but finally she accepted his help. We find the same protective attitude towards cows in Hinduism. The Rig Veda, however, is still ambivalent on this issue. On the one hand, various verses tell us that cows were eaten and sacrificed to the gods, while on the other hand, the word “aghnya,” meaning “not to be killed,” is sometimes used as a synonym for “cow.” 
From 520 BC, we find Ahura Mazda
on inscriptions by the Persian kings. For over a thousand years, Zoroastrianism
became their official religion, until the region was conquered by Islam.