The Old City and its fortress, the Ankara Kalesi, besieged and stormed on many occasions, are built on a 120m/394ft high andesite ridge facing the oldest of Ankara's gecekondu quarters, AltinDag. The foundations are believed to date back to the Galatians. The double walls of the citadel, made from large blocks of stone and pieces of antique masonry, were probably constructed by Michael II (820-29) in the aftermath of two successful assaults by the Arabs under Haroun al-Rachid.
Many of the houses squeezed into the area between the walls are now historic monuments protected by UNESCO.
From the old horse market (At Meydani) where grain and spices are traded, the lower gate, the Hisar Kapisi, with a clock tower, leads into the tortuous alleyways of the outer fortress (dis kale); from there via another gate, the Parmak Kapisi with double bays offset for added security, the inner fort (iç kale) is reached. This probably dates from the time of Heraclius (640/41). The Sark Kale, a tower linking the inner and outer defenses, was strengthened in the ninth century, the resulting walls being up to 8m/26ft thick. It is possible to climb the southeast citadel wall (east tower) at this point, to be rewarded with what is surely the most impressive of all views over the city. On its north side the inner ring wall, once boasting 42 towers, abuts the Ak Kale (or White Fortress) access to which requires a permit from the Department of Antiquities.