tes·tu·do 
(tĕ-stdō, -sty-)
(tĕ-stdō, -sty-)n. pl. tes·tu·dos
1. A Roman siege device consisting of a movable screen protecting the besiegers' approach to a wall.
2. A cover formed by the overlapping shields of besiegers and held over their heads.
[Latin testūdō, tortoise, tortoise shell, testudo, from testa, shell, earthenware vessel, of unknown origin.]