St Mercurius was a Roman soldier of Scythian origin who was born in Cappadocia around the beginning of the 3rd century AD. He converted to Christianity with his parents and changed his name to Philopater. In Arabic, he is known as Abu Seyfain. When he was 17, he joined the Roman army during the reign of Emperor Decius. He became a prominent soldier and won a big battle against invaders with a sword he said was given to him by the archangel Michael. When the emperor asked him to worship pagan gods, St Mercurius protested by saying "I do not worship anyone other than Jesus Christ, my king and my god". Emperor Decius exiled him back to Cappadocia, where he was beheaded and his head was sent to Egypt. The underground city and church named after Saint Mercurius, who is said to have been born in Saratlı, is one of the most popular places to visit in Cappadocia. Three floors of the four-storey St Mercurius Underground City are open to visitors. On the first floor there are three spaces and a passage connecting them. There are two ways out of the second floor. The first exit is a vertical passage called 'Dedeli Dam'. The second exit is a 2.50 metre corridor at the end of the space to the left of the entrance. At the end of the corridor is a water well. One of the four hatches in this space was carved into the floor and the others were formed by opening to the side walls. The third floor is reached by a tunnel. A short, wide corridor leads from the "Arab's Cave" to the church. The church has three naves with two arched columns in the centre. There are 31 graves inside. There is a burial chamber in the south of the side nave northwest of the centre nave. On both sides of the entrance to the burial chamber, different types of motifs were made. The ascent to the third floor is also provided by a tunnel. A short and wide corridor leads from the location known as the "Arab's Lair" to the church of the underground city. The church comprises three naves with two arched columns in the centre. There are 31 graves within the church. There is a burial chamber in the south of the side nave, northwest of the centre nave. On both sides of the entrance to the burial chamber, different types of relief cross motifs were created.