This is one of a series of pictures I took at the At meydanı, or Hippodrome, (opposite the Turkish and Islamic museum on one hand, the Blue Mosque on the other) where they held chariot races in Roman times.
The obelisk is from Karnak in Egypt and commemorates a victory in a 144o BC battle. On the base emperor Theodosius I (379-395) is depicted, with his court, as well as scenes of erecting the obelisk, which was done in 390 AD.