The central hall is constructed with very large stone blocks; limestone interior with sandstone facing.

Strabo visited the Osireion in the first century BCE and gave a description of the site as it appeared in his time: 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.

Strabo then theorises that the Osireion might have been constructed by Ismandes, or Mandes,[a] the same purported builder as with the Labyrinth at Hawara: But if, as they say, Memnon is called Ismandes by the Egyptians, the Labyrinth might be a Memnonium, and the work of the same person who constructed those at Abydos and at Thebes; for in those places, it is said, are some Memnonia.

[4] While, with regard to the depth of the building, its untypical architectural style and its mythological context, there is disagreement as to its true age.

The Egypt Exploration Society (EES) excavations uncovered an ancient mark; “Menmaatre [Seti I] is Benefical to Osiris”.

Graffiti by Egyptian priests of Dynasties XXI–XXII found in the long entrance passage, the vaulted galleries mentioned by Strabo, hint at its function: “The hidden / secret place of the Underworld / Duat of Menmaatre [Seti I]” and more specifically and revealing as the “Birth House of Isis”.