Assassin’s Creed Origins primarily begins in 49 BC.
The game opens in Ptolemaic Egypt during the reign of Cleopatra VII. Bayek of Siwa returns from an assignment and becomes involved in a conspiracy tied to powerful figures in Egypt and Rome. The opening date places the story shortly before Julius Caesar’s arrival in Egypt and the political struggles surrounding Cleopatra.
Origins uses a historical setting at the end of the Ptolemaic period, when Egyptian, Greek, and Roman influences overlapped. Its events lead to the creation of the Hidden Ones, the organization that later develops into the Assassin Brotherhood.
Players sometimes remember 44 BC because Julius Caesar was assassinated in that year, an event referenced in the game’s historical period. However, 49 BC is the year associated with the beginning of Bayek’s main story, not Caesar’s assassination.