[ tɛ'stju:dəʊ , -'stu:- ]
■ noun ( plural ~s or testudines -dɪni:z ) (in ancient Rome) a screen on wheels and with an arched roof, used to protect besieging troops.
↘a protective screen formed by a body of troops holding their shields above their heads.
Origin
ME: from L., lit. 'tortoise', from testa 'tile, shell'.