The Peter and Paul Cathedral is a Russian Orthodox cathedral located inside the Peter and Paul Fortress in St. Petersburg. It is the first and oldest landmark in St. Petersburg, built between 1712 and 1733 on Zayachy Island along the Neva River. Both the cathedral and the fortress were originally built under Peter the Great and designed by Domenico Trezzini. The cathedral's bell tower is the world's tallest Orthodox bell tower. Since the belfry is not standalone, but an integral part of the main building, the cathedral is sometimes considered the highest Orthodox Church in the world.