Roundel (fortification)

The roundel is a strong artillery fortification with a rounded or circular plan of a similar height to the adjacent defensive walls. If the fortification is clearly higher than the walls it is called a battery tower.

The design of a roundel, which was massive in comparison with a normal defensive tower, enabled the deployment of heavy cannon. Roundels were built of both earth and brickwork; in the latter case, vaulted rooms (casemates) were built on the inside.

Roundels appeared in the 15th century when cannon gradually developed into an effective siege weapon. Roundels are the oldest permanent artillery fortifications. Their heyday was in the 15th and early 16th centuries. 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. Other early central European examples that have survived include roundels at Sigmundskron Castle near Bozen (from 1473), at the Hessian water castle of Friedewald (from 1476), the neighbouring Herzberg (from 1477), Haut-Kœnigsbourg from 1479 (Pic. 1), Breuberg (around 1480), in Halle a. d. Saale (from 1484), in Burghausen a. d. Salzach (around 1488), Heidelberg Palace (around 1490/1500), or the southwest roundel of Marburg Castle (1522–23) and in the shape of the Fulda Roundel in front of Kassel Palace (1523).

Like the horseshoe-shaped bastion, the roundel has a so-called blind spot which makes it vulnerable. In addition, the upper level of a roundel had little space for heavy cannon. Even the casemates of a roundel could only house a few cannon because they created a lot of gunsmoke which only dispersed slowly. 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. Even the construction of large and thick-walled roundels like those at Munot in Schaffhausen built from 1563 to 1585, were an insufficient response to the technology of the time.

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