A fortification constructed by the Spanish or Moors appears to have existed on the site before the British capture of Gibraltar in 1704, but the Lines were principally constructed during the 18th century. They were first laid out in 1720, and a stone stepped communication passage was later built to connect them with the Queen's Lines. William Green carried out major improvements after 1761, repairing the parapets, scarping the cliff, repairing the banquets and parapets and smoothing the ditches with mortar. To prevent shells and rubble rolling into the Lines from behind, dry rubble walls were constructed to their rear. The glacis in front of the Lines was also cleared of boulders and crevices were infilled to deny enemy soldiers any shelter. A bombproof barracks, magazine and cookhouse were built at the same time. During the construction of the Lines, an "entire human skeleton" was discovered fossilised in the rock but was blown to pieces by a miner. Nothing else is recorded about this find, but only a few decades later, the first known Neanderthal skull was found nearby.