THERMAL WINDOW

also called therm window in Classical architecture, semicircular window divided into three sections by two mullions, or vertical strips. The base of the central section of a thermal window is wider than that of its two side sections. The thermal window is frequently featured in Renaissance architecture of the 16th century. Because it was especially popular in the works of the influential 16th-century Italian architect Andrea Palladio, it has come to be known as a Palladian motif. The Italians adapted the form of the thermal window from a large, three-part window in the central hall of the Thermae, or Baths, of Diocletian, which were built in Rome in AD 302; this accounts for its other name, the Diocletian window. Thermal windows may also be found in the works of architects of the Renaissance revival of the late 19th and early 20th centuries.