Selene on horseback, from the south side of the Large Frieze.

The Altar, high on a mountainside, was a huge staple-shaped colonnaded structure on a large stepped podium. It was decorated with a frieze 113 metres long depicting the favourite subject of the battles of Gods and Giants, which was no doubt intended by the Pergamene king Eumenes II, who built it, to commemorate his triumphs in Asia Minor and the eastern Aegean. It was seriously damaged in the first century CE, and again in the tenth.

The verve of the figures and composition, and the sheer size, make the frieze one of the landmarks of Hellenistic art. The reliefs are so deep as to be almost freestanding. Today, the sculptures that remain are incorporated into a reconstruction of the altar in the Pergamon Museum in Berlin