This is believed to be the grave of the Apostle or Evangelist Luke who is the author of the Gospel of Luke. At this place is a circular structure and is described as the grave of St Luke because of the bull carved into the door. There are different views of how Luke died, it is not certain. Some have said he was 84 years old and martyred when he met his death by idolaters who tortured him and hanged him on an olive tree in the town of Thebes.
What is interesting with this site. My research tells me that Saint Luke actually died in Thebes, in Greece. and parts of his body are now venerated in Padua Cathedral in Italy. They were moved sometime after 1459, after the fall of medieval Serbian capital Smederevo. This monument is located East of the State Agora and was first excavated in 1865 by J. T. Wood. Apart from a short field campaign in 1908, work on the monument was not re-established until 1997 by the Austrian Archaeological Institute and the Austrian Academy of Science.
At present a final publication is in preparation on the results of that work. Originally built as a fountain in the 2nd century A.D., the building was adapted to a church in Byzantine times (5th-6th century A.D.). After destruction in the 7th century, the church and a cemetery located nearby were kept in use until the Medieval Period. The latest finds at this site date into the 12th-14th centuries. The Byzantine church was built on a high podium on top of a crypt. Polychrome frescoes, mosaic floors and marble decoration indicate the originally rich adornment of the monument.
The graves in and around the crypt support the hypothesis of this being a memorial church to house the relics of a famous saint. Due to the fact that the southern entrance into the crypt was flanked by two pilasters showing oxen and crosses, the building was originally interpreted as the grave of St. Luke, as the bull has traditionally been used as the symbol of St. Luke.