Geographically, France is the largest country in Western Europe and the European Union, and the third-largest in Europe as a whole. With a total population of around 67 million, it is the third most-populous European country. France is a unitary semi-presidential republic with its capital in Paris, the nation's largest city and the main cultural and commercial center. The current Constitution of France, adopted by referendum on 4 October 1958, establishes the country as secular and democratic, with its sovereignty derived from the people. The nation's ideals are expressed in the Declaration of the Rights of Man and of the Citizen, one of the world's earliest documents on human rights, which was formulated during the seminal French Revolution of the late 18th century.