| Arnus Vallis | |
| Coordinates: | 14.1°N -289.5°W |
Arnus Vallis is an ancient river valley in the Syrtis Major quadrangle of Mars, located at 14.1° north latitude and 289.5° west longitude. It is 280 km long and was named after the classical and present day Arno River in Tuscany, Italy (previously named Arena Rupes).[1]