11 arches

West of Castelmadama the Aqua Anio Novus left the valley of the Anio (present Anienne) heading
southwest. At Osteriola there was a splitting (see Ashby pag 268 + fig 27). Here a view on the first
visible part of the branch towards Tivoli. Major parts of the Anio Novus aqueduct were subterranean;
here the channel came to light to cross a small side valley.