The Maritsa or Evros (Марица, Εβρος, Romanized as Hebrus, Meriç) is, with a length of 480 km, the longest river that runs solely in the interior of the Balkans. It has its origin in the Rila Mountains in Western Bulgaria, flowing southeast between the Balkan and Rhodope Mountains, past Plovdiv and Parvomay to Edirne, Turkey. A small section of the northern branch of the river runs entirely in Turkey; it was handed to Turkey in order to prevent the town of Edirne from facing a Greek bank. The rest of the river to the sea flows along the border, near Kastanies, from where it turns south to enter the Aegean Sea near Enez, where it forms a delta. The Tundzha is its chief tributary; the Arda is another one. The lower course of the Maritsa/Evros forms part of the Bulgarian-Greek border and most of the Greek-Turkish border. The upper Maritsa valley is a principal east-west route in Bulgaria. The unnavigable river is used for power production and irrigation.
The places that the river flows through include Pazardzhik, Plovdiv, Dimitrovgrad and Svilengrad in Bulgaria, Edirne in Turkey and Kastanies, Pythio, Didymoteicho and Lavara in Greece. Reservoirs on the Maritsa include the Kiprinos Dam. There are a number of bridges over the river, including the one at Svilengrad, the one west of Edirne in Turkey and GR-2 with the D110/E90 further south and as its border crossings.
In 1371, the river was the site of the Battle of Maritsa, also known as the battle of Chernomen, an Ottoman victory over a Serbo-Bulgarian coalition. Vukašin Mrnjavčević and Jovan Uglješa died in the battle.
Another flood which began from 1 March 2005 flooded several places again and a town which flooded a local school that has a playground leaving the basketball unflooded in Pythio. Several other buildings, roads and streets were also flooded. A day later on 2 March, the flood reached Didymoteicho and Lavara to the southwest. The rainfall amounts to about 5 m, 4.6 m in some areas including the Arda and as high as 6.5 m. Firemen with boats and workers were rescuing and helping people. The rail link to the northern part of Evros prefecture was closed. The flooding of the valley also flooded the Turkish side.
A third round of floods began near Edirne on the Turkish side and Kastanies on the Greek side on 7 March. The river was flowing at nearly 1,000 m³ per second. Kastanies became a lagoon which flooded the entire community including streets and homes and stranded people in their homes. The flood waters merged with the waters of the Arda causing it to flood Kastanies. Farmlands were underwater. The northern branch of the river also flooded houses and properties in Edirne on the Turkish side and several communities around Edirne. Workers put down sandbags to prevent the flooding of properties. The flood later reached the low lying areas of Pythio, Amorio and Lavara along with Didymoteicho. The water level on 8 March was 5.8 m, 5 m at the Kiprinos Dam.
In Greece, one of the barns almost flooded as high as their roofs, several cows and other cattle were affected, some farms lost some cattle. Roads and railways were closed. Flood waters in the eastern part of the Greek prefecture saw water to rise over 6 m. Days later trucks and bulldozers rebuilt several dikes around the area and received help from the government to rebuilt and prevent any flood waters from entering these areas. The cause of the flood was that heavy snowfalls that amounted to record levels occurred in Bulgaria and caused its three dams to overflow in the Arda basin and flooded into the Maritsa. The flood ended a couple of days later but another low-pressure system brought rain to the areas, but it did not create any floods.