Roundel (fortification)

The roundel is an artillery fortification with a rounded or circular plan of a similar height to the adjacent defensive walls.

Early examples of artillery roundels are in the town fortifications of Tábor before 1433 and Sion Castle, that around 1426/27, and certainly before the siege of 1437 were modified.

The roundel was a stage in the development of late medieval fortifications and did not meet the demands of defensive works of the early modern period.

As a result of its disadvantages the roundel was replaced in many places during the 16th century by the acute-angled bastion with a pentangular ground plan based on Italian practice.

Many fortresses consist entirely of interlinked roundels, for example Deal Castle on the south coast of England, the construction of which had been started in 1539.