 Complete the following phrase:  As a physical entity, Potsdamer Platz began as a few country roads and rough tracks fanning out from the Potsdam Gate. According to one old guide book, it was never a proper platz, but a five-cornered traffic knot on that old trading route across Europe. Just inside the gate was a large octagonal area, created at the time of Friedrichstadts expansion in 1732-4 and bisected by Leipziger Straß; this was one of several parade grounds for the thousands of soldiers garrisoned in Berlin at the height of the Kingdom of Prussia. Initially known appropriately as the Achteck Octagon, on 15 September 1814 it was renamed Leipziger Platz after the site of Prussias final decisive defeat of Napoleon Bonaparte at the Battle of Leipzig, 1619 October 1813, which brought to an end the 