Serpent Column, cast to celebrate the victory of Greeks over the Persians during the Persian Wars in the 5th century BC. Constantine ordered the Tripod to be moved from the Temple of Apollo at Delphi, and set in middle of the Hippodrome.
Theodosius the Great, who in 390 brought an obelisk from Egypt and erected it inside the racing track. Carved from pink granite, it was originally erected at the Temple of Karnak in Luxor during the reign of Tuthmosis III in about 1490 BC. Theodosius had the obelisk cut into three pieces and brought to Constantinople. The top section survives, and it stands today where Theodosius placed it, on a marble pedestal. (wikipedia)