The Basilica of Sts. Vitalis, Valeris, Gervase and Protase is commonly named Basilica di San Vitale. It was built in 400 with funds provided by Vestina, a wealthy dowager, and was consecrated by Pope Innocent I in 401/402. The dedication to St. Vitalis and his family (Saint Valeria, his wife, and Sts. Gervasius and Protasius, their sons) is dated to 412.
San Vitale was restored several times, the most important being the rebuilding by Pope Sixtus IV before the Jubilee of 1475, and then in 1598, 1938 and 1960. The church is currently located several metres under the level of the street (via Nazionale), that it faces.
The portico is the most ancient part of the church, possibly dating back to the 5th century. It was altered at the end of the 16th century. The inscription on the portico, with the arms of Pope Sixtus IV, dates from this time. Pope Pius IX built the staircase to the 5th century portico in 1859.
The church has a single nave, with walls frescoed with scenes of martyrdom, among which a Martyrdom of St Ignatius of Antioch, in which a ruined Colosseum is depicted. The apsis, original of the 5th century, is decorated with a fresco by Andrea Commodi, The Ascent to Calvary.
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.