What is a roundel in fortification?
A roundel — also called a rondel — is a thickened, lowered and roughly semicircular projection from a fortification wall, built to mount guns that can sweep along the wall itself, that is, fire in flank. The roundel developed out of the medieval mural tower and is the forerunner of the bastion. The word comes from the Old French rondel, from rond, round.
Why roundels were built
Until the fifteenth century a tall, slender mural tower was ideal: see far, shoot down, hard to scale. With the arrival of gunpowder artillery that very form became a liability. A tall tower is an easy target and collapses once its base is shot away.
The response can be read in the form of the roundel:
- Lowered — often an existing mural tower was literally cut down to wall-walk level so it offered less of a target.
- Thickened — heavy walls and an earth-filled core that absorbs shot instead of shattering.
- Round — a curved face deflects a hit rather than taking it square on.
- Projecting — because the roundel stands forward of the wall line, its guns can fire along the wall and defend its base.
- Casemates with gun loops at the lower level, so fire could also be delivered below the wall-walk.
Why the roundel was superseded
The round form has a basic weakness: directly in front of the curve lies a strip the roundel itself cannot cover — dead ground. An attacker could lodge there against the wall. The answer was the bastion: an angular, pointed work whose every face is fully covered by the neighbouring works. From the late sixteenth century the bastion replaced the roundel.
Application
Roundels today are heritage structures. In Maastricht the roundels Haet ende Nijt and De Vijf Koppen survive; the latter was purpose-built as a roundel rather than converted from a tower.
Managing and repairing this kind of structure raises the same points every time:
- The earth fill is structural. The masonry is a skin around a core of earth and rubble, and that core pushes outwards. Bulging and cracking usually come from this, not from foundation settlement.
- Lime mortar, not cement. Fifteenth- and sixteenth-century brick is soft; a hard joint pushes the moisture path into the brick.
- Drainage on the crown. The top surface of a roundel is large and flat. Without working drainage and a coping, all the rainwater ends up in the core.
Related terms
- Bastion
- Fortification
- Masonry
- Lime mortar
- Listed building
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