Short answers, pulled from the story.
Alexander the Great arrived in Egypt during 331 BC and decided to build a new city on the coast. He used grain from his soldiers' rations to sketch out the streets on the sandy ground before leaving months after founding the place.
The Serapeum of the Great Library was destroyed in 391 when Emperor Theodosius I ordered the demolition of pagan temples. Patriarch Theophilus complied with the imperial request and the neoplatonist philosopher Hypatia was murdered by a Christian mob.
Arabs captured Alexandria in 641 after a siege lasting fourteen months under general Amr ibn al-As. The city received no aid from Constantinople as Heraclius had died and Constans II was only twelve years old.
Cassius Dio recorded that over 20,000 people died during this brutal massacre following insulting satires. Emperor Caracalla ordered his troops to kill all youths capable of bearing arms in 215 AD.
French troops stormed Alexandria on the 2nd of July 1798 during Napoleon's expedition to Egypt. Two French savants estimated the population at between 8,000 and 15,000 people that year.