A dome is an edifice, or more precisely, a portion of an edifice: a hollow hemispherical vault, supported on its outer edges by a circular wall. Domes were found from Roman times, as on the Pantheon, AD 112; by Renaissance times the dome had become a usual architectural feature of a cathedral or mosque.
As an heraldic charge, the dome appears to be unique to Society armory: in such instances, only the dome itself is depicted, with very little of its supporting building. The illustration is taken from Brunelleschi’s dome for the Cathedral of Santa Maria del Fiore, Florence, c.1430 [EB VIII:397].
Andrew of Seldom Rest bears as a badge: Gules, on a bend Or a selle sable, a dome vert, and a rest azure.