Archaeological ruins found in Letoon shows that this sanctuary was founded in the 7th century B.C. It is known that there was an Anatolian goddess and a Nymph cult in the Archaic and Classical Periods (7 - 5 BC). With the Greekization tendency seen in the Hellenistic Period, this cult was replaced by the Leto Cult. During this period, Letoon became the sanctuary of the Lycian Union. Lycia came under the rule of Persians, Carians and Greeks (first Ptolomaios and then Rhodos) respectively.
There are 3 temples side by side dedicated to the goddess Leto, her daughter Artemis and her son Apollo. In the Leto Temple, which was discovered in 1973, the inscription written in three languages belonging to the 4th century BC has Aramaic on one side and Greek and Lycian on the other sides. In the Lycian writings, he writes that "Pixodares ruled this region for the first time as the Karia and Lycian satrap(governor) in 358 BC, established good relations between the Hekotomnid dynasty and the Lycians, and appointed his men as governors to cities such as Lycia, Archon and Xanthos."
Remains and inscriptions show that this place is a religious and political area. There are three temples side by side in the center of the area, but no remains were found above the ground level in any of them. To the east, towards the rocky ridge, there is a temple in the Doric Order, which is a peristylos with 6 x 11 columns measuring 27.90 x 15.07 meters, The temple dedicated to the god Apollo dated to the second half of the 2nd century B.C. The temple consists of pronaos, cella veopisthomodos; the cella walls are decorated with half columns. There is another temple to the west, which belongs to an earlier date and is bigger, 30.25 x 15.75 meters in the Ionic Order, dedicated to the Goddess Leto. This temple is better preserved than the other and most of the pieces allow for reconstruction. Between the two temples, there is another temple dedicated to the goddess Artemis, which is 8.20 x 8.70 meters smaller than the other temples and belongs to an earlier date. To the south of the temples is a church in the form of a basilica that was abandoned in the 7th century AD.
During the excavations to the south and west of the main temple, a large Nymphaion associated with a sacred source was unearthed. The rectangular building built in the east-west direction is delimited by a large, semicircular lined boat and contains two semicircular exedras to the north. The Nymphaion, dated to the 3rd century A.D., was built to replace an earlier Hellenistic building. Excavations were mostly carried out under water, and most of them now remain in the water. A part of this building is under the 6th century church.
There is a large and well preserved Hellenistic theater in the north of the area.
Cevea, which has a northwestern façade, is larger than a semicircle, the middle part was built by cutting the hill slope, and the ends consist of a smooth-surfaced masonry. There is a daizoma and the arched passage on both sides of it opens to the cavea.
The trilingual inscription found in the ancient city contains a text written in Greek, Aramaic and Lycian languages. This inscription was found under the rock layer to the east of the temples. The inscription mentions a cult established in Xanthos for the God Basileus of Caunos. This is the deification of Kaunos, the son of Miletos, who was a legendary city founder. His cult continues until the Roman Period under the title of "king" in Caunos and It has been proved that it existed during the satrapy(governig) period of the brother of Maussollos, Piksodoros, in the 4th century BC. The inscription mentions monthly and annual victims, and it is told that those who oppose the rules are criminalized in front of Leto and her children and the Nymphs.
Strabo says that Letoon is 10 stadia from the mouth of the river and 60 stadion from Xanthos. The first measure he gave may be correct because the coastline has changed since antiquity, but 60 stadia to Xanthos is not correct information. In the city, no traces of ruins from 8 centuries AD can be seen. It is thought that the city was abandoned with the start of the Arab raids. Letoon Ancient City has been on the UNESCO World Heritage List since 1988.