Olbia, situated at the bottom of a deep inlet, is home to Sardinia's main harbour and tourist airport. After the collapse of the Roman empire and with subsequent vandal invasions, it fell to ruin, much like the rest of Sardinia's coastal towns. In the eleventh century, under the dominion of the Pisans settled in Gallura, it was reconstructed on its original site under the name Terranova, which remained in use until 1939. Upon becoming the bishop's see, Olbia enjoyed some rebirth with new maritime traffic and the spread of agriculture throughout the plains. However, its long economic and demographic stagnation continued until the 1800's, when city development once again called for the renewal of the harbour. Roads were then constructed leading out to the state trunk-road 131 and to the train station, and canals were built to contain the rivers directed out to sea. In the 1980's, an impetuous demographic development ensued, further contributed to by a large flow of immigration arriving from the rest of Sardinia and Italy at large, causing Olbia to jump into fourth place in Sardinia's urban hierarchy. Equipped with a small tourist harbour, a Yacht Club and surrounded by many beautiful beaches from north to south, Olbia is also a departure base for excursions to the famous tourist destinations of the north-east coast (Golfo Aranci) and south-east coast up to the Caletta di Siniscola.