COMMENTARY: As we mark the 15th anniversary of the attacks on New York City and Washington, it is worth also remembering that the timing of the attacks was part of the jihadists’ plans.

Mark Twain is supposed to have said, “History doesn’t repeat itself, but it echoes.” As Americans commemorate the 15th anniversary of the Sept. 11 attacks on New York City and Washington, it is worth also remembering that the timing of the attacks on that particular date was part of the jihadists’ plans.

Westerners often forget that the battle with militant Islam has been going on for centuries. While the Islamic religion began in the seventh century as a peaceful, spiritual movement, it soon developed a militant dimension, as the Prophet Muhammad began using military force, first in self-defense and then for conquest. The conquests continued as the Muslim forces pressed westward into Spain and Eastern Europe. At the end of Islam’s first century, the religion had spread from Spain to India.

The Sept. 11 date is significant for jihadists because Islamic forces suffered a major defeat Sept. 11-12, 1683, at the Battle of Vienna. Vienna was the gateway to the rest of Europe, and victory at Vienna meant the Islamic forces could sweep through the rest of Europe, defeating Christianity once and for all. The Turkish army arrived at Vienna on July 14. The Muslims laid siege to the city and demanded that the citizens surrender, renounce Christianity, convert to Islam or pay the required tax of all conquered people. The Islamic forces besieged Vienna for months, while the Christian forces were in disarray and disagreement.

Vastly outnumbered, Vienna’s defenders created an open space around the city walls so the Muslim attackers would be exposed. Meanwhile, the Muslims cut off all supplies, pounded the city with artillery and began digging tunnels beneath the walls. By late summer, Catholic King Jan Sobieski of Poland rallied his troops and headed south. Grand Vizier Kara Mustafa began the final attack on Sept. 11 and celebrated what he knew would be victory by slaughtering 30,000 Christian prisoners.

The Viennese forces fought off the Muslims on Sept. 11 while the armies of Emperor Charles V and Charles of Lorraine began to join in the attack. Muslim mines intended to destroy the walls were located and defused by Viennese soldiers. Meanwhile, King Sobieski’s famous cavalry — the Flying Hussars — were still on their way. Finally, in the late afternoon of Sept. 12, the Polish king ordered the cavalry to attack in four groups, three Polish and one from the Holy Roman Empire: 18,000 horsemen charged down from the hills; it was the largest cavalry charge in history.

The charge broke the lines of the Ottomans and went for Mustafa’s command center. The arrival of the cavalry turned the tide of battle, sending the Muslim Turks into a massive retreat. Within a few hours after King Sobieski’s heroic charge, the Christian forces had won the battle and saved Vienna. Vienna was crucial to world history, because if the Muslim forces had conquered Europe, they would also have controlled the gateway to the New World, and the Americas would have been colonized by Muslims instead of Christians.

However, the Battle of Vienna is not the only important date in the ongoing Muslim-Christian conflict. Just over a hundred years earlier, in May of 1565, a huge armada from the Islamic Ottoman Empire arrived on the shores of the island of Malta in the Mediterranean. Like Vienna, Malta was a stepping stone to the rest of Europe. The little island was defended by the Catholic Knights of Malta, who were vastly outnumbered. The battle raged for months, with the Muslims keeping the island under siege. In the end, the defenders repelled the huge Ottoman attack, and it was on Sept. 11, 1565, that the Muslims returned to their ships and fled.

Two other events in European history marked a Muslim defeat on Sept. 11. For centuries Spain had been dominated by Islam, but in April 1609, King Philip II signed a decree commanding that Muslims be expelled from Spain. A fleet of ships was built to deport them. On Sept. 11, 1609, the decree was promulgated — and over the next years, hundreds of thousands of Muslims were expelled.

Finally, one year after the Battle of Vienna, the Muslim forces were routed again. In 1684, the forces of the Holy League defeated Sultan Mustafa II and the Ottoman army at the Zenta River in present-day Serbia. The Grand Vizier was killed, the Ottoman artillery was lost, and an estimated 30,000 Turkish soldiers were killed or drowned. The Sultan was forced to surrender, and the subsequent Treaty of Karlowitz ceded huge tracts of land in Eastern Europe back to the Catholic House of Hapsburg.

It is politically correct to ignore the religious dimension to world affairs, but it is also naive. We should affirm that not all Muslims are warlike and intent on destroying Christianity, but we should also remember that the violent Islamic extremists see history and current affairs as part of a larger, spiritual battle. The jihadists believe Christianity should be destroyed, and they will not stop until they have accomplished their goal.

Sept. 11 should remind us of the battles that have been fought, the victories that have been won and the fact that the spiritual battle against the forces of evil is not only real — it is not over.

Father Dwight Longenecker is a priest of the Diocese of Charleston, South Carolina.