The ibis catacombs are among the strangest things Egypt produced. At Tuna el-Gebel, at Saqqara and at Abydos, galleries cut into the rock hold mummified ibises in ceramic jars, stacked from floor to ceiling, in numbers estimated at roughly four million at Saqqara and something similar at Tuna el-Gebel.
They are votive offerings. A pilgrim to a shrine of Thoth bought a mummified bird and dedicated it, in the way a pilgrim elsewhere would buy a candle, and the industry that supplied them ran for centuries. Radiography shows that quality control was uneven: some bundles hold a complete bird, some hold a few bones and a lot of packing, and some hold nothing but linen and mud.
Where the birds came from was long assumed to be large-scale farming, and ancient texts mention feeding them. DNA work published in 2019 on birds from several sites found genetic diversity consistent with wild populations rather than a closed captive stock, which suggests seasonal capture from the wild, or at most short-term tending, rather than industrial breeding.
The scale is worth sitting with. This is a religious practice that consumed millions of a single wild bird species over centuries, in the country where that species is now extinct, in honour of the god of measurement and record.