Since the infamous terrorist attacks of 2001, a lot of speculation has been made as to why date September 11th was chosen for the attacks. There appears to be no definitive answer to this question. Those who know the significance are likely dead and if they are not, we have a lot more important questions for them. Some speculate that it is because in America 911 is number we call on our phones for emergencies, which seem completely silly and just a coincidence. Some have said that it was due to the Camp David Accord being signed by Sadat, Carter and Begin in September but that was on the 17th, not the 11th.
Going way back to the 17th century, the Battle of Zenta was fought on September 11th, 1697 when the Hapsburg Imperial Forces made a surprise attack on the Ottoman Empire during the Great Turkish War in what we now know as Serbia. In this attack, which was the last decisive battle of the war, Prince Eugene of Savoy and his troops killed 20,000 Ottomans, took control over Belgrade, seized the Ottoman treasury and took ten of the Sultan's wives captive . After the battle, the treaty of Karlowitz was signed, in which the Ottomans ceded Croatia, Hungary, Transylvania, and Slavonia to Austria. Could this be the date that influenced the terrorists? Could something that happened such a long time ago really hold such significance? Considering the fanatical nature of the people involved, I think it is possible. But it is probably more likely that Sept. 11th from six years earlier that is the date they held more significant.
The Battle of Vienna took place September 11th and 12th, 1683. It is considered by many historians the date on which the West became Christian (as opposed to Muslim) or at least preserved their Christianity for centuries to come. For two months, the Ottoman Empire had been besieging Vienna. If they could take Vienna, they could have possibly sweep through Europe. The King of Poland, Jan III Sobieski, took joint control over the Polish, German and Austrian forces and retook Vienna. Sobieski was called the savior of Western Civilization by the Pope. This was the first of many humiliating defeats for the Ottoman Empire stopping their advances west.
The idea that the date September 11th has no significance is not one that many believe. Fanatics usually don't do anything for no reason including what day to commit mass murder.