Two architectural styles were significant during the Middle Ages- the Romanesque style and the Gothic style.
The Romanesque style is characterized by buildings in heavy masonry, primarily seen in churches and castles. Windows of the period are quite slender, with a semi-circular arch, supporting the masonry in a stable construction. Slanted reveals surrounding the windows lead more daylight into the building.
The semi-circular arch, the colourful stained glass, and decorated reveals are clearly inspired by the architecture of Ancient Rome. The Romanesque window recurs in buildings of the architectural style the Romanesque Revival in the 19th Century.