The entire structure is 35.64 meters wide and 33.4 meters deep; the front stairway alone is almost 20 meters wide. The base is decorated with a frieze in high relief showing the battle between the Giants and the Olympian gods known as the Gigantomachy. There is a second, smaller and less well preserved high relief frieze on the inner court walls which surround the actual fire altar on the upper level of the structure at the top of the stairs. It depicts in a series of consecutive scenes events from the life of Telephos, legendary founder of the city of Pergamon and son of the hero Heracles and Auge, a daughter of the Tegean king Aleus.
In 1878 the German engineer Carl Humann began official excavations on the acropolis of Pergamon, an effort which lasted until 1886. His chief purpose was to rescue the altar friezes and expose the foundation of the edifice. Later, other ancient structures on the acropolis were brought to light. In negotiations with the Turkish government, which participated in the excavation, it was agreed that all frieze fragments found at the time become the property of the Berlin museums.
In Berlin, Italian restorers reassembled the panels comprising the frieze from the thousands of fragments which could be recovered. In order to display the result and create a context for it, a new museum was erected in 1901 on Berlin's Museum Island. As this first Pergamon Museum proved to be both inadequate and structurally unsound, it was demolished in 1909 and replaced with the much larger present museum, which opened in 1930. Although it housed a variety of collections, not least a famous reconstruction of the Ishtar Gate of ancient Babylon, the city's inhabitants also named the new museum the Pergamon Museum after the friezes and reconstruction of the west front of the altar. The Pergamon Altar is today the most famous item in the Berlin Collection of Classical Antiquities, which is on display in the Pergamon Museum and in the Altes Museum, both on Museum Island.