The Grand Duchy of Luxembourg is a landlocked country in western Europe. It is bordered by Belgium to the west and north, Germany to the east, and France to the south. With 576,249 citizens, Luxembourg is among Europe's least populous countries. Its capital, Luxembourg City, is, together with Brussels and Strasbourg, one of the three official capitals of the European Union and the seat of the European Court of Justice, the highest judicial institution in the EU. Founded as a Roman fortress, Luxembourg hosted a vital Frankish castle from the Early Middle Ages. Its climate is oceanic and rainy, especially in late summer, with warm summers and cool winters.