The basilica was probably founded by Pope St Marcus (Mark) in 336, and is one of Rome’s oldest churches. It stand on the site where St Marcus is said to have lived, and was known as the Titulus Pallacinae.
The church was rebuilt in the 5th century, and was left facing the opposite direction.
It was reconstructed in the 8th century by Pope Adrian I (772-795), and given back its original orientation, which it has today. It was flooded when the Tiber rose above its banks soon after, in 791. Pope Gregory IV (827-844) restored it after the flood.