The gateway façade of the monastery is originally 9th century but altered several times up to the 17th century. The entrance itself is through an unadorned archway with a large tympanum, which is now bare but had a fresco of the four martyrs being crowned by an angel in the early 19th century. The squat 9th century brick campanile above is claimed to be the oldest surviving in Rome, although its present appearance dates from 1914.