The Altis (Greek: Ἄλτις) also referred to as the sanctuary to the gods, is the name of a location most well known for being a place of significant religious importance to the Ancient Greeks, considered to be a sacred precinct that was constructed and used from around 776 BCE to fourth century BCE and used for the worship of several Greek gods and goddesses. Though the architects are not definitively known, it is generally attributed to be partially the work of Libon of Elis. Located in the wide valley of the Alfeiós River (also Romanized as Alpheus, Alpheios) in the western part of Peloponnesus, around 18 kilometers away from the Ionian Sea, the name Altis was derived from a corruption of the Elean word alsos meaning “the grove” because the area was thickly wooded with oaks, plane trees, poplars, and olives. The structure itself was an irregular quadrangular area more than 200 yards (183 meters) on each side and walled except to the North where it was bounded by the Kronion (Mount Kronos). Inside were sanctuaries, the centers of religious worship, where the Greeks built over 70 temples, treasuries, altars, statues, and other structures in dedication to their gods. The site was continuously inhabited from Mycenaean times until the 6th century BCE, where cult activity apparently first began at the foot of the hill of Kronos where altars to the goddesses Rhea, Gaia, and Eileithyia have left their traces. Some other cults found here were devoted to figures like the hero cult of Pelops and Hippodameia (arguably the oldest shrine there) important mythological figures that are generally known for the founding myth of the Olympic Games. During the time of the Dorian Invasion settlers from northwestern Greece inhabited the Altis whereby they introduced the worship of two major Greek deities in the Greek pantheon Hera and Zeus as well as constructing the most memorable things there, the Sanctuary and altar of Zeus, where to this day the ruins of the two principal temples: the Temple of Hera (6th century BCE) and the Temple of Zeus (5th century BCE) still remain. Throughout Antiquity this Temple was considered the most perfect example of the Doric order. This sanctuary also contained one of the highest concentrations of masterpieces of the ancient Mediterranean world though many have since been lost. In connection with the cult of Zeus the Altis was then given the name Olympia, with famous Olympia, Greece being built on this site where also the first Olympic Games took place here, once every four years.