Roman Testudo

VINEA, mantlet: The sides were covered with skins or wisker work when required.

The TESTUDO was similar to the VINEA, but squarer and more stoutly built, with
 a sloping roof and/or a shutter on the side next to the enemy's walls: it
was covered over with hides or other non-inflammable substances.

The MUSCULUS was longer, lower, and narrower than the VINEA, forming  a
covered gallery, pushed up at right angles to the enemy's walls.

Reference:

Caesar, G. P, Goold (ed.), H. J. Edwards (trans.), "The Gallic War," (Loeb Classical Library, LCL 72), p. 631