Tambour (French, from Persion tambur), the drummer in the infantry, belonging to the corps of drums. Tambour battant, with drums beating (cf. assault); in the realm of fortification, a small, open-topped, defensible enclosure made of walls or palisades used to flank fortifications, bridges, gates etc.
In Architecture, a tambour designates the cylindrical or multi-faceted prismatic base of a dome, which is typically used to introduce light; the central drum of a carding machine.
Source: Meyers Großes Konversations-Lexikon, 6. Auflage 1905–1909
Tambours are small redoubts of wood (fig. 32) intended to close avenues, gates, and all openings which communicate with the outside. The form of a tambour is that of a small lunette, or redan, according to the place it occupies, and the reverse fires it is intended to afford. If, for example, the gate p, in the wall m o, is to be covered, it will be well defended by a tambour a b c d e, which has the figure of a lunette. The tambour will flank the work, and be at the same time flanked by it. If the wall makes an elbow like m o r, the side might be made straight like that shown at c i.
The circumference of this work is formed by posts 9 or 10 feet long, and 3 inches square at least, when they are to resist musketry only, and not less than a foot when they are to resist heavy field artillery. They are placed vertically like palisades, and made to touch each other exactly. The height from the ground is from 7 to 8 feet, and two rows of loop holes are cut, one at the height of 4 feet 6 inches, the other on the level of the ground, as d (fig. 34). An inner ditch t 3½ feet deep is dug, which leaves a banquette b 2½ feet wide, to fire through the upper loop holes. In this ditch soldiers are placed who fire through the lower loops holes past the intervals of the upper rank. Or the upper row of loop holes is made 6½ high, (fig. 33) and a banquette made of plank, the second row of loop holes is at the height of this banquette, or 2 feet to 2 feet 3 inches. A ditch f is usually made so deep that the enemy cannot reach the upper loop holes, or even the lower one. The slopes of this ditch meet at the bottom, so that the enemy cannot remain covered in it.
Tambours are sometimes covered by a sort of roof, or penthouse, made of joists laid close together, or of several courses of planks, making a thickness of 5 inches, which will resist hand grenades.
Where proper wood cannot be procured, a small crenelled wall is built two feet in thickness.
It may be seen, that by means of tambours, well disposed flanking fires may be obtained, and a straight line, naturally weak, rendered very strong.
Source: Lallemand, Henri Dominique: A Treatise on Artillery (New York 1820)