Decree of Canopus

kuh-NOH-pus

Definition

The Decree of Canopus is an inscription from 238 BCE that records the first known attempt to fix the Egyptian calendar. Egypt's civil year ran a flat 365 days with no leap day, so it slowly slipped against the seasons. At an assembly of priests at Canopus, the priesthood under Ptolemy III decreed adding a sixth extra day every four years to stop the slippage. The reform did not take — Egyptians kept their old drifting 365-day year — but the decree survives because it was carved in three scripts on stone, which later made it a key to reading hieroglyphs.

In Tradition

Historians treat the Decree of Canopus as the earliest documented leap-day proposal, more than two centuries before the same fix finally stuck under Roman rule. It shows the Egyptian priesthood was fully aware that the civil year drifted, and chose, in 238 BCE, to try to anchor it to the seasons and to the rising of Sirius — even though the attempt was abandoned.

In Practice

The decree was issued by a synod of priests gathered at Canopus, in the Nile Delta, on the 17th of the month Tybi in the 9th year of Ptolemy III Euergetes — March 7, 238 BCE. Its calendar clause ordered a sixth epagomenal day (one of the five "days upon the year" added beyond the twelve 30-day months) to be inserted at the end of every fourth year, so the civil year would stop sliding against the seasons and the heliacal rising of Sopdet (Sirius). In practice the change was abandoned and the civil year reverted to its uncorrected 365-day form; the same six-days-every-four-years mechanism was only made permanent in Egypt under Augustus around 26-25 BCE. The decree's lasting importance is partly accidental: like the later Rosetta Stone, it was written out in hieroglyphic, demotic, and Greek, so its trilingual text became one of the documents scholars used to recover the ancient Egyptian scripts.

Historical Origin

Dated to the 17th of Tybi, year 9 of Ptolemy III Euergetes (7 March 238 BCE), issued by a priestly synod at Canopus. Preserved on the Tanis stela, found at San (Tanis) in 1866 by Reinisch and Roesler; a second copy was found at Kom el-Hisn in 1881. The text is trilingual — hieroglyphic, demotic, and Greek. It is discussed in Clagett, Ancient Egyptian Science Vol II, in connection with the epagomenal days and the abortive Sothic fixed-year reform later realized under Augustus.

Definition

In Tradition

In Practice

Historical Origin

Further Reading