Built in 1770–1771 by architects Carl von Gontard and Georg Christian Unger on the orders of King Frederick the Great to celebrate the end of the Seven Years' War.
Modeled after a Roman triumphal arch, featuring two distinct styles on each side—the city-facing side designed by Gontard and the outer side designed by Unger.
There's another Brandenburg Gate in Berlin (built 1788-1791). Both gates share the same name for a simple, practical reason: they were built on the historic country roads that led to the town of Brandenburg an der Havel.
Though built after the one in Potsdam, the one in Berlin has been much more famous.