[5] Although this idea was not taken up, British commanders decided to make the Morass a more substantial obstacle and in 1735, it was dug out and flooded to form a pear-shaped lake connected to the sea via a short channel.

[7] To further restrict access, the British built two defended positions on either side of the northern end of the Inundation, not only to guard against a surprise attack but to prevent desertion by disgruntled members of Gibraltar's garrison.

The Advance Guard Room was built on the east side on the foundations of an earlier Spanish fortification which had controlled movement across the strip of land adjoining the Morass.

"[9] A British clergyman, William Robertson, commented in an 1845 account of a visit to Gibraltar that "while crossing the causeway, the most inexperienced eye is struck with the terrible appearance of the batteries which command it, bristling with cannon, above and around."

"[10] The fortifications around the Inundation became the subject of a bitter dispute in 1789, a few years after the conclusion of the Great Siege of Gibraltar, when works were carried out to improve the North Front defences.

[11] The work was halted and their report unequivocally condemned the project as a bad idea: [T]he removal of the bluff at Forbes's will render it extremely difficult to maintain a post at that pass, which appears absolutely necessary to retard the progress of an enemy and save the garrison from being shut up and insulted by even an interior force.

[11]After the Spanish blockade of Gibraltar ended following the destruction of the Lines of Contravallation in 1810, an increasing number of Spaniards came to work in the territory, travelling to and from it each day as they were not allowed to stay overnight.

Writing in 1914, Horace Wyndham noted that Bayside Barrier would be the first point of assault in the event of a Spanish attack but that "the authorities, however, think it adequately protected by a corporal and three men."

Cabs crowded with three or four families, donkeys and mules staggering under immense loads of fruit and wine-skins, carts and barrows, and men, women and children all appear."

Some 20,000 Spaniards a day crossed the causeway alongside the Inundation to work and sell goods in Gibraltar but were required to go home when a cannon was fired in the evening to signify the closure of the gates.