Villa Features

Thermal windows

 

Conjectural reconstruction of the Baths of Diocletian

Conjectural reconstruction of the Baths of Diocletian Enlarge image

Conjectural reconstruction of the Baths of Diocletian
Andrea Palladio, 1540s
RIBA Library Drawings Collection

Elevation of the entrance front, Chiswick Villa, London

Elevation of the entrance front, Chiswick Villa, London Enlarge image

Elevation of the entrance front, Chiswick Villa, London
Lord Burlington, 1729
RIBA Library Drawings Collection

The thermal or Diocletian window is a very distinctive type, consisting of a semicircular window divided into three lights by two vertical posts or mullions.

The name derives from its appearance in the ancient baths, or thermae, of Diocletian in Rome. Its use was revived by Palladio in the 16th century after his discovery of the window in the Roman emperor’s baths, as shown here in his reconstruction sketch.

Palladio went on to use the window form in many of his buildings, including the Villa Pisani in Bagnolo di Lonigo, although unfortunately the openings of this window are now blocked. They also featured in his two great Venetian churches, San Giorgio Maggiore and Il Redentore, creating striking, well-lit interiors. 

The first known use of a thermal window in English architecture was the re-fronting of Lord Burlington's house at Chiswick, a large Elizabethan mansion. Later, this featured more prominently on the main front to the adjoining villa, now known as Chiswick House. Boldly, above the pediment, a thermal window punctures the drum of the dome, lighting the octagonal room below, at the centre of the building.

After Burlington’s use at Chiswick, the thermal window became a feature almost as common as the Venetian window in Neo-Palladian architecture.