Abdon and Sennen are two martyrs who certainly lived in the 3rd century. Though stories about their lives are legendary, there must be some truth in them. Firstly, they are mentioned by many official documents and martyrologies, which mention the deposition in the Cemetery of Ponziano, on via Portuense, of two Roman saints and martyrs called ‘Abdos et Sennes’. Other well known medieval documents report that many pilgrims arriving in Rome visited via Portuense, entering the basilica where their bodies rested. The unknown author of the passio of the two saints classifies them as Persian princes who, as slaves or freedmen living in Rome, buried martyrs. They were accused by Emperor Decius (200-251) for their work. Since they refused to make sacrifice to idols, they were sentenced to death and taken to the amphitheatre where the Colossal Statue of Nero stood, to be devoured by ferocious beasts but they miraculously tamed the animals. Abdon and Sennen were, therefore, beheaded by gladiators. Their bodies were thrown before the statue of the Sun God and were left there for three days, until the deacon Quirinus collected them and hid them in his house, where they remained for a very long time. Later, as a result of a revelation, they were found and taken to the Ponziano Cemetery. Their relics were then ‘deposited’ in the basilica of S. Marco the Pope, at the time of Pope Sixtus IV (1471-1484). In fact, in 1948 a granite ark was found under the main altar. It contained a large cypress crate with many relics and a parchment dated 1474 indicating the deposition of the relics of saints Mark the Pope, Abdon and Sennen martyrs.