The site of Thermon was inhabited continuously for 1500 years, from the Middle Helladic (early Mycenaean) era until the 2nd c. BC. Built over the remains of Mycenean style megaron, the temple of Apollo had a colonnade made of wood that was later replaced with stone in the Doric style. The design demonstrates the hypothetical development of the Archaic Greek temple from the Mycenaean palace structure with the addition of a peristyle or surrounding colonnade. The interior space had a deep single nave, which was divided in its longitudinal axis by a single row of 12 columns that supported the roof. The temple is famous for the archaic terracotta metopes, ten along the two sides of the temple, decorated with painted scenes from mythology (Hercules?) and are among the earliest examples of this art form in Greece (from 630/20 BC). It represents one of the earliest examples of Doric temple architecture. Below the temple is an even older building from the Geometric period and labeled 'Megaron B.  It too is a long structure set at a slightly different angle than the more recent temple above it. The site was first identified in the late 19th Century by W. J. Woodhouse, subsequent excavations were then carried out by G. Sotiriades and K. A. Rhomaios in the early 20th century.

The sanctuary was destroyed by the Macedonians in 218 BC and again in 206 BC in revenge for the Aetolian's destructions of Dion and Dodona. The site was abandoned after the Roman conquest and the dispersal of the Aetolian League in 167 BC.