The Osirion or Osireon is an ancient Egyptian temple. It is located at Abydos, to the rear of the temple of Seti I. It is an integral part of Seti I's funeral complex and is built to resemble an 18th Dynasty Valley of the Kings tomb.
The Osirion was discovered by archaeologists Flinders Petrie and Margaret Murray who were excavating the site in 1902–3. The Osirion was originally built at a considerably lower level than the foundations of the temple of Seti, who ruled from 1294–1279 BC. While there is disagreement as to its true age, Peter Brand says it "can be dated confidently to Seti's reign", despite the fact that it is situated at a lower depth than the structures nearby, that it features a very different architectural approach, and that it is frequently flooded with water which would have made carving it impossible had the water level been the same at the time of construction.
Strabo, who visited the Osirion in the first century BC, said that it was constructed by Ismandes, or Mandes (Amenemhet III), the same builder as the Labyrinth at Hawara:
"Above this city [Ptolemaïs] lies Abydus, where is the Memnonium, a royal building, which is a remarkable structure built of solid stone, and of the same workmanship as that which I ascribed to the Labyrinth, though not multiplex; and also a fountain which lies at a great depth, so that one descends to it down vaulted galleries made of monoliths of surprising size and workmanship."