The seat of the province has for the most of its history been in the northern reaches of the land, first at Susa (Shush) and then at Shushtar. During a short spell in the Sasanian era, the capital of the province was moved to its geographical center, where the river town of Hormuz-Ardasher, founded over the foundation of the ancient Hoorpahir by Ardashir I, the founder of the Sasanian Dynasty in the 3rd century CE. This town is now known as Ahvaz. However, later in the Sasanian time and throughout the Islamic era, the provincial seat returned and stayed at Shushtar, until the late Qajar period. With the increase in the international sea commerce arriving on the shores of Khuzistan, Ahvaz became a more suitable location for the provincial capital. The River Karun is navigable all the way to Ahvaz (above which, it flows through rapids). The town was thus refurbished by the order of the Qajar king, Naser al-Din Shah and renamed after him, Nâseri. Shushtar quickly declined, while Ahvaz/Nâseri prospered to the present day.