His function as god of beginnings has been clearly expressed in numerous ancient sources, among them most notably Cicero, Ovid, and Varro. As a god of motion, Janus looks after passages, causes actions to start and presides over all beginnings. Since movement and change are interconnected, he has a double nature, symbolised in his two headed image. He has under his tutelage the stepping in and out of the door of homes, the "ianua", which took its name from him, and not vice versa. Similarly, his tutelage extends to the covered passages named "iani" and foremost to the gates of the city, including the cultic gate of the ', named ' or "" from which he protects Rome against the Sabines. He is also present at the Sororium Tigillum, where he guards the terminus of the ways into Rome from Latium. He has an altar, later a temple near the "Porta Carmentalis", where the road leading to Veii ended, as well as being present on the Janiculum, a gateway from Rome out to Etruria.