In ancient Greek architecture, a propylaea, propylea or propylaia (; Greek: προπύλαια) is a monumental gateway. They are seen as a partition, specifically for separating the secular and religious pieces of a city. The prototypical Greek example is the propylaea that serves as the entrance to the Acropolis of Athens. In this case, the propylaea is built wider than the Acropolis of Athens in order to allow chariots through. The construction of it was part of Pericles' great rebuilding program for Athens in c. 437 BCE. The project of the propylaea began once the Parthenon was almost done. It was overseen by Mnesicles (an Athenian architect). Though the work was suspended due to the Peloponnesian War, the important pieces of Mnesicles’ vision were able to come through (World History Encyclopedia). The Greek Revival Brandenburg Gate of Berlin and the Propylaea in Munich both evoke the central portion of the Athens propylaea. The architecture for the propylaea is unique in that it uses horizontal beams across the roof. These beams were supported by marble girders, which were supported by iron bars. The only other known use of metal in Greek architecture for structural purposes is the Temple of Zeus at Agrigento (World History Encyclopedia).