More than two 9/11s.

That date is also the anniversary of the Christian victory over the Ottoman force besieging Vienna in 1683, and, more pertinently, the 1982 withdrawal of international troops that led to the massacres by Phalange forces of Palestinians living in the Sabra and Shatila refugee camps in Lebanon. In his 2002 "Letter to America", Osama bin Laden identified the latter incident as a particularly severe insult.