aspis
The Aspis ( /ˈæspɨs/; Ancient Greek: ἀσπίς) is a very big and rounded bronze shield used by the ancient hoplite Greek warriors from the city of Sparta.
Its big size was due to the fact that it was designed to protect the user from the neck to the lower leg.
It was also intended to protect both the soldier and the comrade beside him (to the left) in a Phalanx battle formation. That's why they were always used in the left hand in those occasions.