Archaeological finds at Letoon shows that the sacred place established in seventh century B.C. During the Archaic and Classical periods (7th-5th century BC) the site was probably sacred to the cult of an earlier mother goddess and a Nymph (female water deity), which were later superseded by the worship of Leto as a result of Hellenizing tendency during Hellenistic period. In this period Letoon became a sanctuary of Lycian League. Lycia came under the sovereignty of Persians, Greeks and Carians (first Ptolomaios, and then Rhodes) respectively.

According to a legend told by Ovid the Latin poet, the nymph Leto was loved by Zeus and gave birth to her twins fathered by him, Artemis and Apollo on the island of Delos. Then she came where the Xanthos River reaches the sea and walked by the river until she reached riverhead. She wanted to wash her children there but blocked by the peasants so she turned them into frogs for revenge. That is why Leto Temple was built in this place on behalf of the goddess Leto where locals turned into frogs. The truth behind this legend is the possibility of existence of a water source dedicated to an Anatolian goddess. And then the same water source became a sanctuary on behalf of Leto, Artemis and Apollon.

Moreover, Letoon Trilingual Stele discovered in 1973 during the archeological exploration of the Letoon temple complex, near Xanthos, ancient Lycia. It belonges to 4th century BC and Aramaic, Greek and Lycian inscriptions exist on its each face separately. Lycian inscriptions tells that; “Pixoderes as being Caria and Lycia satrap, ruled the region for the first time in 358 BC, established good relations with Hekotomnid dynasty, assigned his men to be governors to Lycia, Archon and Xanthus. 

Remaining ruins and inscriptions shows that this place was religious and political area. At the center of this area there are three temples side by side, but no remain has been found yet over the ground level of any of them. On the east side towards the rocky ridge, the Apollo Temple exists in the Doric style and it is 27.90m by 15.07m and has 6 x 11 columned peristlos dates back to 2nd century BC.  Temple consists of pronaos, cella and opisthomodos. The walls of cella are decorated with half-columns.


Further on to the west, there is a temple dedicated to goddess Leto belonged to an earlier date. It is the largest and best preserved temple and is in the Ionic order, having dimensions of 30.25 x 15.75 m. Its remaining pieces allow reconstruction of large part of it. It was also peripteros of 11 by 6 columns and the cella walls were decoratedwith half-columns.  
Between those two temples, the oldest and the smallest of the three temples stands and measures 18.20 by 8.7 meters. It was dedicated to Goddess Artemis.
To the south of temples, there is a church in the form of a basilica abandoned in the 7th century BC.  

During the excavations took place to the south and west of the main temple, a large Nymphaeum which was connected to a sacred spring was unearthed. The rectangular building constructed in the east - west direction was bordered with a large, coated boat which is in the form of a half circle. It contains two half-circular exedras on the north. The Nymphaeum dates back to 3rd century BC and it was built on an earlier Hellenistic structure. Excavations carried out mostly under water and major portion still remains in the water today. A section of this building is under a 6th century church.         
On the north of this area there is a large and well preserved theater constructed in the Hellenistic period. Cevea facing the northwest is larger than a half circle shape and its middle part was carved from the bedrock of the hill slope. The edges are formed of smooth masonry. There is one diazoma and the vaulted gates on the either sides of it openes to the cevea.
The texts on the trilingual stele found in this ancient city were written in Aramaic, Greek and Lycian languages. It was found under a layer of rock east of the temples. The inscription is a public record of a decree authorizing the establishment of a cult in Xanthus, with reference to the deity called Basileus, the god from Caunus. This was to deify Caunos who was the son of Miletos and the legendary founder of the city. His cult was perpetuated under the name of 'king' in the city of Caunus until the Roman period and its existence was proved in 4th century BC during Pixodoros satrapy who was brother of Maussollos. Inscriptions also mentions about monthly and annual sacrifices and those who were against the rules, in front of Leto, her children and the nymph were deemed guilty.
Strabon tells that Letoon was 10 stadion far from the mouth of the river and 60 stadion far from Xanthus. His first measurement might be true because the coastline has changed since the ancient period but the second measurement about Xanthus is not correct.   
There is no trace of remain dating after the 8th century BC. It is believed that the city was abandoned with the beginning of the Arab raids.
The ancient city of Letoon is a UNESCO World Heritage Site since 1988.

This project is co-financed by the European Union and the Republic of Turkey