The zodiac was not revealed. It was compiled, standardized, mathematized, and then repeatedly re-anchored by calendar reform. This is the sequence.

Date	Event
c. 1900–1600 BCE	Old Babylonian star lists and the Prayer to the Gods of the Night name constellations that survive into the zodiac — the Bull, the Scorpion, the Goat-Fish among them.
c. 1100 BCE	The "Three Stars Each" texts (Astrolabe B) sort 36 stars into the paths of Ea, Anu and Enlil, three bands across the sky. The first systematic celestial bookkeeping.
c. 1000 BCE (contested; some place the underlying observations c. 1300–1000 BCE)	MUL.APIN is compiled — a two-tablet Babylonian compendium of star lists, risings, intercalation rules and shadow tables. Its list of the "stars in the path of the Moon" gives seventeen or eighteen constellations along the ecliptic. This is the direct ancestor of the zodiac, but it is not yet twelve, and the divisions are not yet equal.
686 BCE	The oldest surviving dated copy of MUL.APIN. The text is older than the tablet.
7th century BCE	Enūma Anu Enlil, the roughly seventy-tablet omen series, is in canonical use. Celestial divination is temple and palace work, read for the king and the land — not for private individuals.
5th century BCE, commonly c. 450–400 BCE (contested; J. P. Britton argued for c. 400 BCE)	Babylonian astronomers replace the ragged constellations with twelve equal signs of 30 degrees each. This is the actual invention of the zodiac as a measuring scheme.
410 BCE	The earliest dated horoscope yet identified, a Babylonian cuneiform tablet casting a birth. Astrology turns from the fate of kingdoms to the fate of a person.
331 BCE onward	Alexander's conquest opens sustained Greek access to Babylonian scholarship.
c. 280 BCE (tradition, contested)	Berossus, a Babylonian priest of Bel, is said by Vitruvius to have taught Chaldean astral doctrine on the island of Kos. The story is late and may be legend, but it stands for a real transmission.
c. 275 BCE	Aratus's Phaenomena versifies the constellation scheme of Eudoxus of Cnidus and becomes the standard Greek and Roman sky poem.
c. 150–120 BCE (dating contested)	The pseudonymous Nechepso–Petosiris texts appear in Ptolemaic Egypt — the founding literature of Hellenistic astrology, fusing Babylonian signs with Egyptian decans and Greek geometry.
c. 127 BCE	Hipparchus of Nicaea discovers precession, comparing his measurement of Spica with observations made about 150 years earlier by Timocharis. He puts the drift at not less than one degree per century. His treatise is lost; we know it because Ptolemy reports it.
45 BCE	The Julian calendar takes effect. Its 365.25-day year runs about eleven minutes long, so the equinox slips earlier against the dates by roughly one day every 128 years.
c. 150 CE	Ptolemy's Almagest — the star catalogue of 1,022 stars in 48 constellations, and the explicit statement that the signs are reckoned from the equinox, not the stars. The tropical zodiac is now fixed by definition.
c. 150–170 CE	Ptolemy's Tetrabiblos gives astrology a physical rationale in Aristotelian terms and becomes the base text of the Western tradition for fourteen centuries.
c. 285 CE	The conventional epoch at which the tropical and sidereal zodiacs coincided under the Lahiri definition. Everything after this is drift.
325 CE	The Council of Nicaea works from an equinox on 21 March. The date is now embedded in Easter reckoning, which is what will eventually force a calendar fix.
4th–6th centuries CE	Zodiac wheels appear in synagogue floor mosaics at Hammat Tiberias and Beth Alpha, complete with a Helios figure at the hub.
787–886 CE	Abū Maʿshar al-Balkhī writes the Great Introduction, the most influential Arabic systematization; Latin translations by John of Seville (1133) and Hermann of Carinthia (1140) carry it back into Europe.
1582 CE	The Gregorian reform. Inter gravissimas is issued on 24 February; 4 October is followed directly by 15 October, dropping ten days to pull the equinox back to 21 March. Britain and its colonies do not follow until 1752. Because the tropical zodiac is anchored to the equinox, the reform is what keeps the sign dates roughly where they are.
1922 / 1930 CE	The IAU fixes 88 constellation names, then adopts Eugène Delporte's boundaries. The ecliptic now demonstrably crosses thirteen constellations, Ophiuchus included — a fact about lines on a chart, not a lost sign.
1890s–1917 CE	Alan Leo strips horoscopy down to sun-sign character reading, making mass-market astrology possible.
24 August 1930 CE	R. H. Naylor's column in the Sunday Express, written on the birth of Princess Margaret, launches the newspaper sun-sign column — the form almost everyone now means by "zodiac".

In Mesopotamia this was religion, straightforwardly. The sky was legible because the gods wrote on it, and reading it was a licensed profession: the ṭupšar Enūma Anu Enlil, the scribe of the omen series, reported to the palace. Ishtar was Venus, Nergal was Mars, Marduk was Jupiter — not symbols of those planets but those planets. The omens concerned the king, the harvest, the enemy and the flood.

The Greek layer sits on top of that and behaves differently. Attaching Chrysomallos to Aries, or the Nemean lion to Leo, is mostly Hellenistic literary tradition — catasterism, the business of Eratosthenes' Catasterismi and Hyginus's De Astronomia, which collect and tidy stories rather than record worship. There are exceptions worth naming: the Dioscuri behind Gemini had genuine cult at Sparta and at Rome, and the Babylonian gods behind Taurus, Capricorn and Aquarius were receiving offerings in temples long before any Greek wrote them down. But nobody sacrificed to Libra.

Christian writers argued with the zodiac rather than ignoring it. Augustine attacked it on free-will grounds in the Confessions and City of God, leaning on the case of twins born under one sky to opposite fates; church councils barred clergy from practising it. It survived anyway, absorbed rather than erased — as the labours of the months in cathedral portals and books of hours, and as the tetramorph, where the four fixed signs (bull, lion, eagle-for-scorpion, man-for-water-bearer) become the four Evangelists of Ezekiel and Revelation. In the Islamic world ʿilm aḥkām al-nujūm was a serious mathematical discipline with serious opponents; Ibn Sīnā and al-Ghazālī both wrote against it, and Maimonides condemned it outright in his Letter on Astrology of 1195.

Rulers below are the traditional seven-planet rulerships — the ones the site displays. Modern astrology reassigns Scorpio to Pluto, Aquarius to Uranus and Pisces to Neptune, but those are twentieth-century additions.

Sign	Dates	Glyph	Element	Modality	Ruler
Aries	Mar 21 – Apr 19	♈	Fire	Cardinal	Mars
Taurus	Apr 20 – May 20	♉	Earth	Fixed	Venus
Gemini	May 21 – Jun 20	♊	Air	Mutable	Mercury
Cancer	Jun 21 – Jul 22	♋	Water	Cardinal	the Moon
Leo	Jul 23 – Aug 22	♌	Fire	Fixed	the Sun
Virgo	Aug 23 – Sep 22	♍	Earth	Mutable	Mercury
Libra	Sep 23 – Oct 22	♎	Air	Cardinal	Venus
Scorpio	Oct 23 – Nov 21	♏	Water	Fixed	Mars
Sagittarius	Nov 22 – Dec 21	♐	Fire	Mutable	Jupiter
Capricorn	Dec 22 – Jan 19	♑	Earth	Cardinal	Saturn
Aquarius	Jan 20 – Feb 18	♒	Air	Fixed	Saturn
Pisces	Feb 19 – Mar 20	♓	Water	Mutable	Jupiter

The four cardinal signs open the seasons at the equinoxes and solstices. The four fixed signs hold their middles. The four mutable signs hand over to the next.

The chip in the breadcrumb bar reads the sign from a fixed table of month-and-day boundaries, not from an ephemeris. Real ingresses wander by a day or so from year to year, because the tropical year is not a whole number of days and the equinox slides around inside 20–21 March. The table takes the conventional dates and holds them steady.

That is the right trade for what this is. The strip is a cultural display — seven ways different people have divided the same year, shown side by side — not a prediction and not an astronomical instrument. If you want the Sun's true ecliptic longitude, use an ephemeris. If you want to know what the Babylonians, the Greeks, the Mughal court astrologers and a 1930 London newspaper all thought late March was for, the strip is the point.

• World Zodiacs — the other six systems in the strip.
• Vedic Zodiac — the sidereal counterpart, about 24 degrees behind these dates.
• Calendar — the live month grid.
• Religion — the wider religion section.
• Culture — the parent section.