Remember that even back in Roman times, today's New District was the place where Western-oriented minorities settled. When Franciscan priests came here in the 13th century, they built a church in the Galata district . That church became known as the Hagia Sophia of the Roman Catholic minority in Constantinople, which was then mostly Eastern Orthodox. After that church burned down in the late 17th century, the Franciscans chose to rebuild on this site. The current Neo-Gothic building, with a particularly impressive facade, dates from 1912. St. Anthony's still serves an active Roman Catholic congregation with weekly Mass, and the Christmas service here has become a major social event in Istanbul, attended by Turkey's jet set (even many Muslims). If the church is open, feel free to take a look inside. (s3)

Located on istiklal Street in Beyoğlu, the Saint Antoine Church is on the left side of the street if you are facing from Galatasaray towards Tünel.
Construction began in 1906 and the church was completed in 1912. It's architect, Giulo Mongeri, who was born in Istanbul, gave it an Italian Neo-Gothic style. Today it is Istanbul's largest church with the busiest congregation and is run by Italian priests. The Church was built in a courtyard. The entrance of the church is on the main street between two apartments which were built to earn money for the church. (s2)