They occupy a natural ledge which overlooks the landward entrance to Gibraltar and were an extension to the north-east of the King's Lines.

They run from a natural fault called the Orillon to a cliff above the modern Laguna Estate, which stands on the site of the Inundation, an artificial lake created to obstruct landward access to Gibraltar.

[2] The Lines were built in 1788[1] but the Spanish or Moors seem to have constructed a much earlier irregular defensive wall on the same site, as depicted in a 1627 map by Don Luis Bravo de Acuña.

During the tenure of William Green as Gibraltar's Senior Engineer from 1761–83, the Lines were repaired, improved and fortified, and the cliffs below were scarped to make them impossible to climb.

[1] They saw action during the Great Siege of Gibraltar (1779–83) when the Lines were a principal target for Spanish gun batteries; during a heavy bombardment in September 1782, they suffered significant damage.