What is the longest river in Europe?

The Volga, about 3,530 kilometres, entirely within Russia - and it does not reach an ocean. It drains into the Caspian Sea, which is landlocked, so the largest river in Europe is part of an internal basin rather than a route to the sea.

It carries an enormous share of Russian identity, called Volga-Matushka, Mother Volga, and roughly half the Russian population lives in its basin. It was also the line at Stalingrad: the German objective was to reach it and cut the country's main north-south artery, and the fighting through the winter of 1942 was the point at which the eastern front turned.

It is now a chain of reservoirs rather than a river. Eight large dams built through the Soviet period turned it into a series of lakes for hydroelectricity and navigation, drowning towns and about 700,000 people's homes in the process - the flooded town of Mologa still emerges in dry years. The dams also broke the sturgeon runs, which is a substantial part of why Caspian sturgeon and the caviar trade that depended on them collapsed.