The Lines of Contravallation of Gibraltar, known in English as the "Spanish Lines", were a set of fortifications built by the Spanish across the northern part of the isthmus linking Spain with Gibraltar. They later gave their name to the Spanish town of La Línea de la Concepción. The Lines were constructed after 1730 to establish a defensive barrier across the peninsula, with the aim of preventing any British incursions, and to serve as a base for fresh Spanish attempts to retake Gibraltar. They played an important role in the Great Siege of Gibraltar between 1779 and 1783 when they supported the unsuccessful French and Spanish assault on the British-held fortress. The siege was ended after the lines of contravallation were attacked by British and Dutch forces under the command of the Governor of Gibraltar, General Augustus Eliot. The attack caused the Spanish forces to retreat and abandon the fortifications and the combined British led forces virtually destroyed all the Spanish gun batteries and the enemy cannon and munitions either captured or destroyed. This attack is still commemorated to this day and is known as 'Sortie Day'.