Susa, Piedmont in the context of "Henry of Segusio"

The Susa Valley (Arpitan: Vâl Susa; Piedmontese: Valsusa; Occitan: Val d'Ors; Italian: Val di Susa; French: Val de Suse) is a valley in the Metropolitan City of Turin, Piedmont region of northern Italy, located between the Graian Alps in the north and the Cottian Alps in the south. It is one of the longest valleys of the Italian Alps. It extends over 50 kilometres (31 mi) in an east-west direction from the French border to the outskirts of Turin. The valley takes its name from the city of Susa which lies in the valley. The Dora Riparia river, a tributary of the Po, flows through the valley.

A motorway runs through the valley from Turin to Chambéry in France through the Fréjus tunnel or by crossing the Col du Mont Cenis (2083m), and to Briançon, also in France, over the Col de Montgenèvre.

The Arch of Augustus is an important monument constructed in the city of Susa, Piedmont, in the province of Turin. It was originally built at the end of the 1st century BC to record the renewed alliance between Emperor Augustus and Marcus Julius Cottius, a Celto-Ligurian ruler who had been made king and Roman prefect of the Cottian Alps. The arch, together with other remains from the period, such as the Roman amphitheatre and a Roman aqueduct, underscore the importance that the city of Susa had during the Roman period.

The Dora Riparia (Italian: [ˈdɔːra riˈpaːrja]; Piedmontese: Dòira Rivaira; French: Doire Ripaire or Doire; Latin: Duria minor) is an alpine river, a left-bank tributary of the Po. It is 125 kilometres (78 mi) long (of which 5 km is in France), with a 1,231 square kilometres (475 sq mi) drainage basin. It originates in the Cottian Alps, close to the Col de Montgenèvre in France, where it is called the Piccola Dora. Its name becomes the Dora Riparia after the confluence with the Ripa in the Argentera Valley and the Thuras de Bousson close to Cesana Torinese.

Further down the valley, in Oulx, the river grows thanks to its main upper tributary, the Dora di Bardonecchia, and before Susa is augmented by the Galambra and Cenischia. After Susa, it only receives minor tributaries: from the left, Gravio by Condove, Sessi by Caprie, and Messa by Almese, from the right Scaglione by Meana and Gravio by Villar Focchiardo. It runs through the Susa Valley, and after having crossed part of the plain of the Po and the territories of the comunes of Avigliana, Alpignano, Pianezza and Collegno, joins the Po at Turin. It is considered a "stream" (torrente) until Susa, and a river (fiume) to Turin.

Marcus Julius Cottius was King of the Celtic and Ligurian inhabitants of the mountainous Roman province then known as Alpes Taurinae and now as the Cottian Alps early in the 1st century BC. Son and successor to King Donnus, he negotiated a dependent status with Emperor Augustus that preserved considerable autonomy for his country, making him a Roman governor, and adopted Roman citizenship.

The March or Marquisate of Turin was a territory of medieval Italy from the mid-10th century, when it was established as the Arduinic March (Latin: marca Arduinica). It comprised several counties in Piedmont, including the counties of Turin, Auriate, Albenga and, probably, Ventimiglia. The confines of the march thus stretched across the Po Valley from the Western Alps in the north, to the Ligurian Sea.

Because of the later importance of the city and valley of Susa to the House of Savoy, whose members styled themselves as "marquises of Susa", the march is sometimes referred to as the March or Marquisate of Susa. Yet in the tenth and early eleventh centuries, the city and valley of Susa were not the most important part of the county, let alone the march, of Turin. Successive members of the Arduinici dynasty were documented far more frequently in their capital, the city of Turin, than anywhere else, and until the late 1020s, Susa was controlled by a cadet branch of the dynasty, rather than by the marquises themselves.