Pergamon
Pergamon's other notable structure is the great temple of the Egyptian gods Isis and/or Serapis, known today as the "Red Basilica" (or "Kızıl Avlu" in Turkish), about south of the Acropolis at (39 7' 19" N, 27 11' 1" E). It consists of a main building and two round towers within an enormous "temenos" or sacred area. The temple towers flanking the main building had courtyards with pools used for ablutions at each end, flanked by stoas on three sides. The forecourt of the Temple of Isis/Sarapis is still supported by the Pergamon Bridge, the largest bridge substruction of antiquity.
Pergamon
The city gradually declined during Late Antiquity, and its settled core contracted to the acropolis, which was fortified by Emperor Constans II (). In AD 663/4, Pergamon was captured by raiding Arabs for the first time. As a result of this ongoing threat, the area of settlement retracted to the citadel, which was protected by a 6-meter thick wall, built of spolia.