William Smith, A Dictionary of Greek and Roman Antiquities, John Murray, London, 1875. p 297-299.

CLIPEUS (a)spi/j), the large shield worn by the Greeks and Romans, which was originally of a circular form, and is said to have been first used by Proetus and Acrisius of Argos (Paus. ii.25 §6), and therefore is called clipeus Argolicus (Virg. Aen. iii.637), and likened to the sun. (Compare also a)spi/da pa/ntos7) e)ishn, Hom. Il. iii.347, v.453, a)spi/daj eu)ku/klouj, xiv.428; Varr. De Ling. Lat. v.19, ed. Müller; Festus, s.v.). According to other accounts, however, the Greeks obtained the shield, as well as the helmet, from the Egyptians (Herod. iv.180; Plat. Tim. p24b). The shield used by the Homeric heroes was large enough to cover the whole man. It was sometimes made of osiers twisted together, called i0te/a, or of wood: the wood or wicker was then covered over with ox hides of several folds deep, and finally bound round the edge with metal (Hom. Il. xii.295). The outer rim is termed a!ntuc (Il. xviii.479), i1tuj (Eur. Troad. 1205), perife/reia or ku/kloj. [ANTYX.] In the centre was a projection called o)mfa/loj or mesomfa/lion, umbo, which served as a sort of weapon by itself, or caused the missiles of the enemy to glance off from the shield. It is seen in the next woodcut, from the column of Trajan. A spike, or some other prominent excrescence, was sometimes placed upon the o)mfa/loj, which was called e)pomfa/lion.