San Pedro church is believed to be located over a previous edifice housing the remains of the Córdoban martyrs Januarius, Martial and Faustus, dating to the 4th century AD. After the conquest of the city by king Ferdinand III of Castile (1236), a church dedicated to St. Paul was built here in his program of construction to give a Christian appeal to the previously Muslim city. Construction began in the late 13th century and was completed in the early 14th century.
The edifice's current appearance date mostly to later restorations. Part of the bell tower and two of the medieval gates have survived, a new one having been added by architect Hernán Ruiz II in 1542. In 2006, the church was elevated to the status of minor basilica by Pope Benedict XVI.
References:The Walls of Constantinople are a series of defensive stone walls that have surrounded and protected the city of Constantinople (today Istanbul) since its founding as the new capital of the Roman Empire by Constantine the Great. With numerous additions and modifications during their history, they were the last great fortification system of antiquity, and one of the most complex and elaborate systems ever built. They were also the largest and strongest fortification in both the ancient and medieval world.
Initially built by Constantine the Great, the walls surrounded the new city on all sides, protecting it against attack from both sea and land. As the city grew, the famous double line of the Theodosian Walls was built in the 5th century. Although the other sections of the walls were less elaborate, they were, when well-manned, almost impregnable for any medieval besieger.