Vienna is the capital of the Republic of Austria and also one of the nine states of Austria. Vienna is Austria's primary city, with a population of about 1.7 million, it is by far the largest city in Austria, as well as its cultural, economic, and political centre. It is the 10th largest city by population in the European Union. The English name of Vienna, the German name Wien, and the names of the city in most languages, are thought to be derived from the Celtic name of a settlement, but opinions vary on the precise origin. Some claim that the name comes from Vedunia, meaning "forest stream", which subsequently became Venia, Wienne and Wien. Others claim that the name comes from the name of the Roman settlement Vindobona, probably meaning "white soil" or "white property", which became Vindovina, Viden and Wien. Founded around 500 BC, Vienna was originally a Celtic settlement. In 15 BC, Vienna became a Roman frontier city (Vindobona) guarding the Roman Empire against Germanic tribes to the north.