The Loire is the largest river in France, spanning over 1, 000 kilometers from its source in the Massif Central to its mouth at the Atlantic Ocean. It is the longest river in France and the second longest in the European Union. The Loire is also known for its many tributaries, including the Allier, Cher, Indre, Vienne, and Sèvre Nantaise. The Loire Valley is a UNESCO World Heritage Site and is home to many of France's most famous châteaux.