 The relative abundance of Spanish dams below is due partly to more intensive field work there; for Italy only the Subiaco Dams, created by emperor Nero (54–68 AD) for recreational purposes, are attested.These dams are noteworthy, though, for their extraordinary height, which remained unsurpassed anywhere in the world until the Late Middle Ages.The most frequent dam types were earth- or rock-filled embankment dams and masonry gravity dams.