Alexander the Great's Diary was located by Rick, Evelyn, and their son Alexander O'Connell, in an abandoned Hindu temple along the Indus River in India. Unfortunately while Jonathan Carnahan was trying to pry a gem from a statue's forehead, he unknowingly set off a booby-trap which resulted in the diary being destroyed.
The diary was owned by Alexander the Great, he wrote in it detailing his daily life during his conquests in Northern Egypt. In his entries he referenced to having the Scrolls of Thebes with him, which he checked out from the Library of Alexandria.
One of the entries stated that Alexander left the sacred Scrolls of Thebes in the Palace of Merneptah in the ancient Egyptian city of Memphis. But then a later entry states that he put the scrolls on the Greek Warship the Athena, for "Safe keeping."
After being found, the booby-trap set off by Jonathan caused the ceiling of the temple descend in an attempt to crush those present. Alex used the diary to stop the ceiling from crushing his uncle, but as a result the diary was destroyed.