The river Ladonas originates from Arroania and specifically from Mount Penteleia (also known as Dourduvana). Its sources are in the area of the village of Lycouria in the area called 'Rachi Pyrgos' or 'Kefalovryso' where it gushes through sinkholes with such force that it could drive 20 mills at the same time, as mentioned in 1906, which made it impassable even in the summer months.

It crosses the prefecture of Achaia and Arcadia and contributes to the river Alpheus. Its length is more than 60 km and its riverside on the map looks like a coiled snake. Its tributaries are the Aroanios or Katsanas, the Paos or Paios or Xeropotamos, and the Tragos or Daraiko river. Near its confluence with the Alpheus, it is also called 'Roufias.

It was famous since ancient times for the beauty of its landscape and for its fish. Pausanias, visiting the area in the 2nd century AD, mentions it as the most beautiful river there is.

The ancient Arcadians had deified the river and claimed that it was the son of Ocean and Tethys. The nymphs Daphne and Metopi are also mentioned as his daughters. According to mythology, the goddess Demeter was washed in its waters to purify herself after an unintentional union with Poseidon, while Artemis hunted on its banks. Pan once wandered near the river and there Pan saw and loved the nymph Syringa and began to hunt her. Ladon wanted to help her and turned her into a reed. Then Pan cut some reeds and by joining them together he made the Syringa, a musical instrument that only he used.