The large Hellenistic temple had two predecessors from archaic times. One building dates from around 700 B.C., the other from the 6th century B.C. Even then, the complex was given a ring hall supported by columns, the shape of which anticipated the Hellenistic sanctuary. Since the archaic sanctuary lies under the stone masses of the Hellenistic temple, relatively little is known about it. In the temple courtyard remains of the previous buildings can still be seen.

The construction of the Hellenistic sanctuary began around 330 BC.
It is associated with the conquest of Miletus by Alexander the Great in 334 B.C. and the incorporation of Didymas into the Polis Miletus.
The ring hall rises on a seven-level substructure, the Stereobat. Its entrance is in the east and leads over an open staircase of 14 steps.
From there, after passing through the ring hall, you reach the vestibule. Two tunnel vaults lead into the interior of the temple at the side of the portal. These tunnels are the only entrances. Translated with www.DeepL.com/Translator

Inside the temple there is a courtyard where the foundations of a building measuring 8,24 m × 14,23 m are located. This building served to protect the Kultmal, a freshwater spring.
On the east side of the courtyard, between the two tunnel passages mentioned above, an open staircase with 24 steps leads to a three-door wall. This wall has two Corinthian half-columns and forms an exterior and facade architecture within the courtyard.
Behind it is a hall with two opposite stairwells and the so-called Great Portal. With a height of 50 centimetres, the thresholds are relatively high and could only be crossed with aids.
Although the temple was worked on for about 600 years, it was never completed. The last smoothing of the walls was not carried out. Thus extensive antique work drawings remained there, which were only discovered in 1979. These are obviously work plans for columns, beams and other details. The lines are carved into the surface of the marble blocks with metal gravers, rulers and compasses and are accurate to a few millimetres.
Together with Delphi, Dodona and Klaros, Didyma was one of the most important Greek oracles. The last great heyday of the sanctuary was in the 1st and 2nd centuries.

In Greek and Roman mythology, Apollo is the god of light, healing, spring, moral purity and temperance, as well as prophecy and the arts, especially music, poetry and song; he was also the god of healing and the god of archery. Born in Didyma, the son of Zeus, the father of the gods, and Leto, the goddess (Latin: Latona), like his first-born twin sister Artemis (Latin: Diana), he belonged to the Olympic gods, the twelve main gods of the Greek pantheon. The sanctuary in Delphi, the most important oracle site of antiquity, was consecrated to him.

Tunnel corridor into the inner courtyard