A simile is an explicit comparison between two unlike objects. Similes are quite common & frequent in all kinds of poetry. Milton's PARADISE LOST is an epic, and epic/Homeric similes substantially contribute to its grand, elevated style. Epic similes are sustained and elaborate comparisons first employed by Homer; that's why they are called 'Homeric' similes.
In PARADISE LOST(book1), you may consider those lines in which Satan, lying in the gulf of fire, is compared to the mythical Leviathan deluding the mariners on the Norwegian sea.The simile goes on and on for some ten lines, the primary explicit point of similarity bwtween them being their monstrous hugeness. But the Miltonic simile goes beyond the explicit to become functional and proleptic. Just as the Leviathan deceived the sailors by pretending to be an island and therefore a safe shelter for them, Satan is also a deceitful creature having deluded the angels, and subsequently the parents of mankind.