Ottomans considered Jews and Christians as the people of the Book since all three worshipping the same Abrahamic God. Hence, the location of the Patriarchate of Constantinople (the Pope of the Eastern Orthodox Church) has stayed the same even after the conquer of Constantinople, modern day Istanbul.
Atheism as it is is today rather a new concept. In Ottoman Empire the person who claimed that there was no God would be considered insane.
In Europe and the Near East, until the nineteenth century the common wisdom was that our existence was irrefutable evidence for the God’s existence, which made “there is no God” an irrational statement; one might as well said “I don’t exist”.