[1] 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.

Only 25 years later they were effectively abandoned by the Spanish as the Peninsular War recast France as Spain's enemy and Britain as its ally.

During the negotiations that led to the Treaty of Utrecht of 1713, under which Spain ceded Gibraltar to Britain, the British government sought to compel the Spanish to cede "a convenient quantity of land round Gibraltar, viz., to the distance of two cannon shot ... which is absolutely necessary for preventing all occasions of dispute between the Garrison and the Country ..."[3] The Spanish government adamantly refused and would agree only to cede "the town and castle of Gibraltar, together with the port, fortifications and forts thereto belonging", explicitly rejecting any suggestion that Britain had any claim over the isthmus.

"[4] When work began on the Lines of Contravallation, the British again asserted that "although territorial jurisdiction was not ceded with the Fortress of Gibraltar by the Treaty of Utrecht, it is a recognised maxim and a constant usage in favour of fortified places, that the ground commended by their cannon pertains to them ..."[5] Once again the Spanish rejected this; the Spanish Secretary of State, the Marquis de la Paz, replied to a British démarche to point out that the "cannon shot rule" had not been agreed in the treaty, and that in any case "the ordinary range of cannon is 200 to 250 toises and the line is set more than 600 toises' distance from the fortress".

[6] The building works continued despite British protests that it was a hostile act and demands, which the Spanish ignored, that the lines should be removed to a distance of 5,000 yards from the fortress walls.

Lieutenant Colonel Thomas James of the Royal Artillery, writing in his 1771 History of the Herculean Straits, provided a detailed description of each of the forts and bastions.

Its pentagonal structure was aimed like an arrowhead south at Gibraltar and supported 24 gun positions, with a bastion trace in the gorge, a dry ditch, a covered way and a glacis.

[1] James recorded that its rampart was "thirty feet broad, and mounted with twelve iron fifteen pounders, and one thirteen inch brass mortar."

[19] In January 1809, the Spanish commander in the region, General Francisco Castaños y Aragón, ordered the garrison of the Lines to strip them of all stores and ammunition, to be shipped to Barcelona and Valencia to support the defence of those cities against the French.

[20] Lieutenant-General Colin Campbell, the Lieutenant-Governor of Gibraltar, obtained permission from the Supreme and Central Junta of Spain in Seville to dismantle the Lines.

[18] Campbell ordered Gibraltar's senior engineer, Colonel Sir Charles Holloway, to carry out preparations for destroying the Lines.

By the start of February the French Imperial Army's 1st Corps, commanded by Marshal Claude Victor-Perrin, was outside Cádiz only 62 miles (100 km) from Gibraltar.

After an advance column of 200–300 Spanish soldiers arrived in Algeciras on the far side of the bay, Campbell gave the order to go ahead with the demolitions.

As a report in The London Chronicle noted, "every part of the garrison facing the Spanish Lines was crowded with Spectators, to witness the explosion which was truly grand and picturesque ... the entire front of [Forts San Felipe and Santa Bárbara] being blown into the ditch, and the whole rendered a complete mass of ruins.