The BC/AD (or BCE/CE) year numbering comes from the Anno Domini system developed in late antiquity, which used Roman numerals and did not include a concept of “year 0.” As a result, the sequence goes … 2 BCE, 1 BCE, 1 CE, 2 CE, with no zero in between.
This matters for calculating time gaps across the BCE/CE boundary: you must account for the missing zero-year. In the Cleopatra vs. Great Pyramid comparison, sources like Encyclopaedia Britannica place Cleopatra’s death in 30 BCE and the Great Pyramid’s completion in the early 25th century BCE (c. 2500s BCE), and the “no year zero” convention is part of why careful cross-era arithmetic is needed—though it does not change the direction of that comparison.