In ancient Greek architecture, a propylaion, propylaeon or, in its Latinized form, propylaeum—often used in the plural forms propylaia or propylaea (/prɒpɪˈliːə/; Greek: προπύλαια)—is a monumental gateway. It serves as a partition, separating the secular and religious parts of a city. The prototypical Greek example is the propylaea that served as the entrance to the Acropolis of Athens. The Greek Revival Brandenburg Gate of Berlin and the Propylaea in Munich both evoke the central portion of the Athens Propylaea.

The Greek word προπύλαιον, propylaeon (propylaeum is the Latin version), is the union of the prefix προ-, pro-, "before, in front of", plus the plural of πύλη, pyle, "gate", meaning literally "that which is before the gates", but the word has come to mean simply "gate building".

The propylaea were the monumental gates to the Acropolis, commissioned by the Athenian leader Pericles in order to rebuild the Acropolis at the conclusion of the Greco-Persian Wars. These propylaea were built wide enough to allow chariots through. The construction 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 the Athenian architect Mnesicles. Though the work was suspended due to the Peloponnesian War, the important pieces of Mnesicles' vision were able to come through. The architecture is unique in that the horizontal beams across the roof 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.

The oldest known freestanding propylaeum is the one located at the palace area in Pasargadae, an Achaemenid capital.^[1]

A covered passage, called "the Propylaeum", used to face the Palace of Darius in Susa.^[2]

In the 18th century, the Athenian Propylaea inspired Carl Gotthard Langhans in construction of the Brandenburg Gate in Berlin.

• Portal (architecture)
• Triumphal arch
• Gate tower

• Berve, H.; Gruben, G.; and Hirmer, M. Greek Temples, Theaters, and Shrines (New York, 1963). A general look at selected Greek structures.
• Dinsmoor, William Bell (1922), "Structural Iron in Greek Architecture", American Journal of Archaeology, XXVI.
• Dinsmoor, W. B., The Architecture of Ancient Greece (New York, 1975 – but actually a reprint of the 1950 publication). A general book on Greek architecture; dated in many areas but valuable for the Propylaea.
• Dinsmoor, W. B. Jr., The Propylaia I: The Predecessors (Princeton, 1980). A careful study of the predecessors of the Propylaea.
• Eiteljorg, Harrison, II, The Entrance to the Acropolis Before Mnesicles (Dubuque, 1993). A careful study of the predecessors of the Propylaea, with very different conclusions from those of Dinsmoor above.
• Lawrence, A. W., Greek Architecture (Baltimore, 1973). A general book on Greek architecture.
• Robertson, D.S. Greek and Roman Architecture' (Cambridge, 1969). A general book on Greek and Roman architecture. Available in paper, this may be the best place to begin for those with no knowledge of ancient architecture.
• Travlos, J., Pictorial Dictionary of Ancient Athens (London, 1971). An encyclopedic approach to the monuments of Athens.
• The Perseus Project. An electronic resource that provides quick information, but some of the information about the Propylaea was incorrect when the site was last checked. Several good photographs of the Propylaea are available through the Perseus project.
• Cartwright, Mark. "Propylaea". World History Encyclopedia, Https://Www.worldhistory.org#Organization, 24 July 2022, https://www.worldhistory.org/Propylaea/.

• Propylaea.org – leads to a variety of material, some scholarly, but many photographs as well