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
For the altar's construction, the required flat area was skillfully created through terracing, in order to allow it to be oriented in relation to the neighbouring Temple of Athena. The base of the altar measured around 36 x 33 metres and was decorated on the outside with a detailed depiction in high relief of the Gigantomachy, the battle between the Olympian gods and the Giants. The frieze is 2.30 metres high and has a total length of 113 metres, making it the second longest frieze surviving from antiquity, after the Parthenon Frieze in Athens. A 20 metre wide staircase cut into the base on the western side leads up to the upper structure, which is surrounded by a colonnade, and consists of a colonnaded courtyard, separated from the staircase by a colonnade. The interior walls of this colonnade had a further frieze, depicting the life of Telephus, the son of Heracles and mythical founder of Pergamon. This frieze is around 1.60 metres high and thus is clearly smaller than the outer frieze.