Troyes is located on the Seine river about 150 km (93 mi) southeast of Paris. This area is known as the Champagne region of Northern France. Many half-timbered houses (mainly of the 16th century) survive in the old town. Troyes has been in existence since the Roman era, as Augustobona Tricassium, which stood at the hub of numerous highways, primarily the Via Agrippa. In medieval times Troyes was an important international trade centre, centring on the Troyes Fair. The name troy weight for gold derives from the standard of measurement evolving here. The winters are cool and the summers are warm to hot with moderate rainfall all year.