For many centuries, sacred ibis, along with two other species in lesser numbers, were commonly mummified by the Ancient Egyptians as a votive offering to the god Thoth. Thoth, whose head is that of an ibis, is the Ancient Egyptian god of wisdom and reason, and thus of truth, knowledge, learning and study, and writing and mathematics. The sacred ibis was considered the living incarnation of Thoth on earth. Pilgrims from all over Egypt brought thousands of ibis offerings to four or more main temples, which at their peak mummified and buried thousands of birds a year in gigantic and ancient catacombs (one complex was in operation for 700 years). Eventually, an estimated eight million birds were mummified and entombed by the Ancient Egyptians.