The cult of Apis stretches back to the very beginning of Egyptian civilisation, to the time of Menes, the first pharaoh who united Upper and Lower Egypt around 3000 BCE. In those earliest centuries the Egyptians watched the black bulls of the delta with a mixture of fear and reverence, for the bull was the strongest creature in the land, the symbol of virility and raw power that no man could tame. But the Apis was not merely a strong bull. He was a god incarnate, the ba, the living soul of Ptah, the divine artificer of Memphis who created the world through the power of his heart and tongue. Ptah was the patron of craftsmen, the god who shaped metal and stone, and the Apis embodied his creative force in flesh and blood, walking among the people as proof that the divine was not distant but present, breathing, eating, and lowing in the temple courtyard.

The selection of a new Apis was a sacred science conducted by the priests of Ptah at Memphis. When the old bull died, the priests searched the entire kingdom for a black calf born from a cow that had been impregnated by a flash of lightning or a beam of moonlight, a miraculous conception that proved the god had chosen his own vessel. The chosen bull had to bear twenty-nine sacred marks: a black body, a white triangle or diamond upon the forehead, the figure of an eagle or vulture upon its back, a knot of flesh beneath the tongue shaped like a scarab, and a double tuft of hairs at the end of its tail. Its mother was given the title "Isis cow" and was venerated in her own right, buried in a separate catacomb near the Serapeum when her time came. The new Apis was brought to Memphis on a boat decorated with gold and flowers, and the entire nation celebrated his arrival, for the birth of a new Apis meant that the god had not abandoned Egypt.

Once installed, the Apis lived in a palace adjoining the temple of Ptah at Memphis, a building of fine stone and painted columns where he was attended by a staff of priests, fed on the choicest grains and vegetables, and given a harem of the most beautiful cows in the land. His birthday was celebrated with a seven-day festival during which the streets of Memphis filled with music, dancing, and the sacrifice of oxen that were beheaded and offered to the bull as lesser gods might offer tribute to a greater. But the Apis was not merely an object of worship. He was an oracle, and his behaviour was interpreted as divine will. When petitioners approached him, the priests watched his movements with intense attention: a step forward meant approval, a turn away meant refusal, a lowing at a particular moment could decide the outcome of a war or the fate of a dynasty. Alexander the Great visited the Apis before his conquest of Persia, and the Roman emperor Titus presented offerings to the sacred bull, acknowledging that in Egypt, the god walked on four legs.

When the Apis died, the entire kingdom entered mourning. For seventy days the Egyptians shaved their heads, abstained from meat, and wore sackcloth, and the bull's body was embalmed with the same techniques used for pharaohs. His viscera were removed and placed in canopic jars, his flesh was treated with natron and resin, and he was wrapped in the finest linen. Then began the funeral procession from Memphis to Saqqara, a solemn march that carried the mummified bull across the desert to the Serapeum, the underground burial complex that would be his eternal home. The Serapeum was begun under Amenhotep III of the Eighteenth Dynasty around 1400 BCE, but it was Prince Khaemweset, the fourth son of Ramesses II, the great builder king of the Nineteenth Dynasty, who excavated the first underground gallery, the Lesser Vault, to house the sarcophagi of future bulls. Eight centuries later, Psamtik I of the Twenty-Sixth Dynasty expanded the complex into the Greater Vault, a tunnel three hundred metres long lined with twenty-four chambers, each one containing a granite sarcophagus hewn from a single block and weighing between forty and seventy tons. The Egyptians lowered these monstrous coffins into place by filling the chambers with sand, placing the sarcophagus on top, and then digging the sand away from beneath until the stone settled onto the floor, a technique so precise that one sarcophagus was abandoned in the tunnel, left there for reasons that remain a mystery to this day.

After death, the Apis was not merely dead. He became Osiris-Apis, the fusion of the bull and Osiris, the god of the dead and resurrection, and his soul was believed to join the underworld journey of the sun. In the Ptolemaic period, after Alexander the Great conquered Egypt, the Greeks fused this Egyptian deity with their own Zeus to create Serapis, a bearded god who wore the modius, a basket-shaped headdress, and who became the patron deity of Alexandria and the Greco-Roman world. The cult of Serapis spread across the Mediterranean, and temples to the fused god were built from Britain to Mesopotamia. But in Egypt, the old practice continued. The last known Apis bull died in the reign of the Roman emperor Diocletian in the late third century CE, and the Serapeum was finally closed by order of the emperor Augustus, who reportedly declared that he worshipped gods, not cattle. Christians later vandalised the vaults, smashing the commemorative stelae and scraping the inscriptions from the sarcophagi in an effort to erase the pagan cult. Yet the memory of the Apis endured, and when the French archaeologist Auguste Mariette rediscovered the Serapeum in 1850, he found the massive granite coffins still standing in their chambers, silent witnesses to the god who had lived and died three thousand years before.