The Old Town of Vilnius is the historical centre of Vilnius, about  in size. Its history begins from the Neolithic period. During it, the glacial hills were intermittently occupied and a wooden castle, at the confluence of the Neris and Vilnia rivers, was built around 1000 AD to fortify Gedimino Hill. The settlement developed into a town in the 13th century, when the pagan Baltic people were invaded by the Westerners during the Lithuanian Crusade. Around 1323, when the first written sources about Vilnia occurred, it was the capital of the Grand Duchy of Lithuania, which was formed from various cultures and nationalities residents. At this time, it only had some brick structures. By the 15th century, the Grand Duchy of Lithuania had become one of the most powerful and the largest country in Europe with its territory stretching from the Baltic Sea to the Black Sea (mostly, present-day Belarus, Ukraine and Russia lands). The historic centre consists of three castles territories (Upper, Lower and Curved) and the area that was previously encircled by a Wall of Vilnius. Its plan is mostly circular with its center in the original castle site. The streets pattern is medieval and has small, narrow streets, however large squares were also developed in later periods. Pilies Street, the main artery, links the Palace of the Grand Dukes of Lithuania with Vilnius Town Hall. Other streets meander through the palaces of feudal lords and landlords, churches, shops and craftsmen's workrooms.