A Calendar That Drifted Through Every Season It Named

The consequence of having no leap day was not a minor inconvenience but a slow unmooring of the calendar from the reality it was built to track. Over the centuries, the month the calendar called the start of the inundation season could fall in any actual season at all, since the error compounds relentlessly and the names Akhet, Peret and Shemu described increasingly little about the weather or the Nile on the ground.

Ptolemy III attempted a fix in the Decree of Canopus of 238 BCE, proposing an extra day every fourth year on the later Julian pattern, but Egyptian priestly and administrative resistance meant the reform was never generally adopted in his lifetime. It took Augustus's annexation of Egypt and his calendar reform of 26 BCE, imposing the Julian leap year rule onto the old Egyptian month structure, to finally fix the drift, and that fixed version is the direct ancestor of the Coptic calendar Egyptian Christians still keep. The unreformed civil calendar itself is no longer kept by anyone: it belongs to history rather than to any living community, though its month names, its thirty day structure and its five epagomenal days survive almost unchanged in the Coptic and Ethiopian calendars that inherited its shape while finally correcting the flaw that had made it drift.