Answer:
In 1529 and again in 1683, Vienna was seriously threatened by the Ottoman Empire. The Ottomans were a powerful Muslim empire that controlled much of southeastern Europe and the Middle East. In 1529, they laid siege to Vienna for two months, but they were eventually defeated by the Holy Roman Empire. In 1683, the Ottomans again laid siege to Vienna, but they were defeated by a coalition of European forces led by the Holy Roman Empire and Poland. The defeats at Vienna marked the beginning of the decline of the Ottoman Empire.