The Arachthos River is the eighth longest river in Greece, with a total length of 135 kilometers. Its source is in the Pindus mountains, near the town of Metsovo and its mouth is 16 kilometers southeast of Arta, near Kommeno. Over the centuries the alluvial deposits have transformed the north shore of the Ambracian Gulf and have created numerous lagoons. The river is famous for its approximately 55 stone bridges, some of which have become legendary such as the bridge of Arta. The Plaka Bridge was the largest one-arch bridge in the Balkans but it collapsed during a major flood in 2015. In the past the river was navigable from its mouth all the way to Arta.