The Shield of Heracles is an archaic Greek epic poem that was attributed to Hesiod during antiquity. The subject of the poem is the expedition of Heracles and Iolaus against Cycnus, the son of Ares, who challenged Heracles to combat as Heracles was passing through Thessaly. It has been suggested that this epic may reflect anti-Thessalian feeling after the First Sacred War (595–585 BCE): in the epic, a Thessalian hero interfering with the Phocian sanctuary is killed by a Boeotian hero (Heracles), whose mortal father Amphitryon had for allies Locrians and Phocians. This was a pastiche made to be sung at a Boeotian festival at midsummer at the hottest time of the dogstar Sirios. To serve as an introduction, fifty-six lines have been taken from the Hesiodic Catalogue of Women. The late 3rd- and early 2nd-century BCE critic Aristophanes of Byzantium, who considered the Catalogue to be the work of Hesiod, noted the borrowing, which led him to suspect that the Shield was spurious.