Portugal exhibits sharp topographic contrasts. Although the north is largely lowland or land of medium altitude, the distribution of highlands is unequal north and south of the Tagus (Tejo) River. From north to south, the principal mountain ranges are the Peneda (reaching a maximum height of 1,416 m/4,646 ft), Gerêz (1,507 m/4,944 ft), Marão (1,415 m/4,642 ft), Montemuro (1,382 m/4,534 ft), the Açor (1,340 m/4,396 ft), and Lousã (1,204 m/3,950 ft), all north of the Tagus. The uplands of Beira, traversed by the Tagus on its way to the sea, contain Portugal's highest peak, Estrêla (1,991 m/6,532 ft). Westward lies the low coast of the Beira Littoral. The Tagus and Sado basins lie adjacent to the hilly area of Estremadura and rise to the hills of Alentejo on the east. The interior lowland of lower Alentejo, farther south, is limited by the hills of Algarve. The south coast, from the mouth of the Guadiana to Cape St. Vincent, is mainly steep, but northward from Cape St. Vincent to the Tagus, including the great Bay of Setúbal and the estuary of the Tagus, the coast is low. North of the Tagus, it rises steeply toward the hills of Sintra, beyond which is a low coast of dunes interrupted by the marshes of Aveiro. Beyond the mouth of the Douro River, the coast is steep all the way to the Spanish frontier and the mouth of the Minho River. The larger rivers—the Minho, the Douro, the Tagus, and the Guadiana—all rise in Spain. The Douro has the longest course in Portugal (322 km/200 mi).