"Cross-domed units", a more secure structural system created by bracing a dome on all four sides with broad arches, became a standard element on a smaller scale in later Byzantine church architecture. The Cross-in-square plan, with a single dome at the crossing or five domes in a quincunx pattern, became widely popular in the Middle Byzantine period (c. 843–1204). It is the most common church plan from the tenth century until the fall of Constantinople in 1453. Resting domes on circular or polygonal drums pierced with windows eventually became the standard style, with regional characteristics.