A remnant of the Roman and Byzantine era of Constantinople is the Hippodrome or At Meydanı (Horse Square). It was initially built by the Roman Emperor Septimius Severus, but it was Constantine The Great who remodeled and extended it. The Hippodrome was the center of Byzantium's public life for 1,000 years and of Ottoman life for 400 years. The Hippodrome was an immense structure of 480 metres in length and 117.5 metres wide, it could held up, according to one estimate, about 100,000 people. the central line, or spina, around which chariots raced, was adorned with an array obelisks, columns and statues. Only three of these monuments survive in what is now called the Sultanahmet parkı. The ancient Hippodrome extended beyond the boundaries of the present square. The northern end of the Hippodrome, where chariots and spectators entered the arena, was located where now stands the Kaiser Wilhelm Fountain. The semi-circular southern end of the arena is concealed beyond the buildings at the south end of the present square.
Four monuments at today's At Meydanı are worth noting. At the northern end, there is the gift of the German Emperor Kaiser Wilhelm to Sultan Abdül Hamit II in 1901, the Kaiser Wilhelm Fountain also known as Alman Çesmesi. Of considerable older age is the Obelisk of Theodosius also named Dikilitaş . It was originally commissioned by Pharaoh Thutmose III, who had it erected at Deir el-Bahari opposite Thebes in Upper Egypt, to commemorate one of his campaigns in Syria and his crossing of the Euphrates River. The obelisk, which now has a height of nearly 20 metres, lost one third of it length during tranportion. According to Sir William Matthews Flinders Petrie (Flinders Petrie, WM. (1896). A History of Egypt: Volume 2, Cambridge University Press, Cambridge, UK), its original height including pedestal was 56 m (185 feet) and it had an estimated weight of 800 tonnes. It was shipped to Constantinople by the Emperor Julian, between 361 and 363 AD by a ship specially made for this purpose, but it could not be raised and lay for several years on the seashore. It was finally erected on top of a 6 metre marble base by Theodosius I in 390 AD. Sculptured reliefs on this base depict Theodosius I and his family as they look down at various events taking place on the Hippodrome.
Another structure on the spina is a strange spiral column that comes up out of a hole in the ground. This Serpentine Column or Yılanlı Sütun was once much taller and was topped by three serpent heads. It stood in front of the temple of Apollo in Delphi, where it was erected to commemorate the victory of the Greeks over the Persians in Platea at 479 BC. The column was brought to Constantinople by Constantine the Great.
A third structure on the square is a rough stone obelisk the Walled Obelisk, also known as Column of Constantine VII Porphyrogenitus and locally as Ormetaş. The emperor Constantine, after whom it is named, had it sheathed with gold-plated bronze, but the column itself was of considerable older age, perhaps that of Theodosius the Great or even that of Constantine the Great. The ornamentation bronze plates were carried off to Venice when the Crusaders sacked the city in 1204.
Here are the photos of the Hippodrome, click on the thumbnails to see greater pictures
South of the hippodrome, hidden like a precious jewel is the Sokullu Mehmet Paşa Camii. It was built in 1571-1572 at the height of Ottoman Architecture by the famous Ottoman architect Mimar Sinan for Ismihan Sultan, daughter of Sultan Selim II and wife of the Grand Vezir Sokullu Mehmet Paşa. The mosque is built on the site of an ancient church of which the columns of the courtyard were taken. The courtyard is beautifully designed with a fine şadırvan (oblivion fountain) in the middle. As in many mosques it served as a medrese with the scholars living in little domed cell under the portico. The interior of the mosque is decorated with the finest Iznik tiles and contains, framed in gold, four fragments from the sacred Black Stone in the Kaaba at Mecca. The marble pillars flanking the mihrab can revolve and do so when the foundations are disturbed by an earthquake, thus acting as an early warning device.