Vulcan's festival, the Volcanalia, fell on 23 August, in the dry heat of late summer when the danger of fire in barns and harvest was greatest. Its rites reflect exactly that fear: bonfires were lit, and Romans threw small live fish, or, in some accounts, other small animals, into the flames, offering these creatures to the god as substitutes in the hope that he would spare human life and property from burning. Because his power was dangerous, Vulcan's temples were characteristically sited outside the sacred boundary (the pomerium) of the city and of settlements, keeping the fire-god, symbolically, beyond the walls. This deliberate placing on the margins is one of the clearest expressions in Roman religion of a god approached mainly to avert the harm he could do.
Vulcan's name had one more scientific life still to come. In the mid-nineteenth century the astronomer Urbain Le Verrier, fresh from his triumphant prediction of Neptune, proposed that an unseen planet, which he named Vulcan, orbited even closer to the sun than Mercury and explained a small, otherwise unaccounted-for irregularity in Mercury's orbit. Decades of searching produced no confirmed sighting, and the puzzle was finally resolved in 1915 when Albert Einstein's general theory of relativity accounted for Mercury's orbital anomaly without requiring any additional planet, quietly retiring the hypothetical world named for the Roman fire-god after some sixty years of intermittent astronomical hunting.