Mictlan is the lowest and most general underworld of Aztec cosmology, the destination of the great majority of the dead, those who died of ordinary causes, as opposed to the select who went to the sun's paradise (warriors and sacrificial victims), to Tlalocan (those taken by water and rain), or to the nurse-tree heaven for dead infants.
Ruled by the skeletal death-god Mictlantecuhtli and his consort Mictecacihuatl, it lay in the far north and deep below, and reaching its final rest was not immediate but a grueling four-year journey through nine successive levels, each with its own hazard: rivers to cross, clashing mountains, obsidian winds that cut like knives, fields of blades. The dead were buried or cremated with goods to aid the passage, and, in a striking custom, with a dog to help them across the deepest river. Only after completing all nine levels did the soul reach Mictlan proper and dissolve into final repose. The conception is notable for what it lacks: the destination in the Aztec afterlife was determined chiefly by the manner of death rather than by moral conduct in life, so Mictlan is neither a punishment nor a reward but simply the common end of an ordinary death, a hard road to a quiet oblivion. Its imagery survives, transformed, in the modern Mexican Day of the Dead.