In 1839, the British government began reviewing the state of its overseas fortifications. On 4 November 1839, Lord John Russell, Secretary of State for the Colonies, directed that the defences of Gibraltar, Bermuda, and St. Helena be examined by a special committee. The committee reported back on 12 May 1840—a remarkably swift turnaround for a government body.

One of its members was the distinguished Royal Engineer, Major General Sir John Jones, KCB. In October 1840, he was sent to Gibraltar by the Master General of the Ordnance to carry out a detailed inspection of the Rock’s defences, a task that kept him there until June 1841.

General Sir John Jones’s report, extending to roughly 250 pages, was accompanied by several maps and plans, though not all have survived. Regarding Windmill Hill and the communications leading to Queen’s Gate, Jones proposed that:

“Quarters for officers should be added to the existing barracks on Windmill Hill, and that these barracks should be made defensible.”

Jones recommended the construction of a line of retrenchments at the head of Windmill Hill to block any potential enemy advance from Europa Point up the peninsula. The hill provided a naturally strong defensive position capable of enfilading the road from Europa. As Jones observed, “Two hundred men on Windmill Hill and Europa Pass ought to hold as many thousands at bay.”

As part of his recommendations, and to ensure secure communication between Buena Vista and the roads across the gorge of Windmill Hill, Jones proposed to scarp (cut away and steepen) the remaining sections of rock or to raise the wall along its summit. This would provide a minimum height of 40 to 45 feet along the entire stretch between Buena Vista and the double flank on the eastern Mediterranean side of Europa, creating a continuous and compact defensive line from the Mediterranean to the Bay and strengthening the South Front.

With the proposed scarping, every part of Windmill Hill’s outer contour would become so steep and inaccessible that the interior line across the gorge would serve mainly as an enclosure wall with flanked trace—intended to provide cover and support for any part of the garrison forced to retreat from the outer defences and regroup to repel the enemy.

This interior line was considered essential to the overall defensive system of the upper Rock. It formed the left flank of the upper communication network, while the scarped rock on its right connected directly to the defensive wall along the road from the Town through Queen’s Gate, together forming a continuous barrier against any attempted ascent of the Rock’s southern and western faces.

The Retrenchment Block and flanking demi-bastions covering the Windmill Hill Flats, 1861-63 War Department and Admiralty properties map.

The line was designed for simplicity and efficiency. A small fleche (arrow-shaped outwork) projected forward to protect troops retreating from Buena Vista or Europa, helping to maintain order under fire. Structurally, it was intended to be little more than a loopholed wall.

This arrangement met the recommendations of the Master General and the Committee, ensuring that the barracks at Windmill Hill were fully defensible. The officers’ quarters were incorporated into the defensive perimeter, and a glacis (a gentle protective slope) was added along the entire front of the Retrenchment block, including the two flanking bastions.

Additional measures were also planned. The gateway through the Moorish wall behind the eastern flank was to be fitted with a couvre-port (covered passage for protection), while the existing Moorish defences were to be repaired and defended by a line of firing loops for infantry accessed by means of a spiral staircase. This flank was designed in the form of a demi-bastion. A gun position was erected above the arched couvre-port.

The western gate, forming the right flank of the line, also required reinforcement—all of which were included in the overall project plan. This was achieved by the construction of another bastion with four-gun emplacements in addition to the infantry firing loops on the right flank. The 1861–1865 Ordnance Survey map shows four platforms and embrasures on this right flank, and one on the left flank. The retrenchment itself is loopholed along almost its entire length, reflecting its design for active defence.

Remains of the glacis on the right flank.

Archway and looped wall defenceson left flank demi-bastion.

The main works recommended in the Jones Report were carried out using convict labour. In 1842, HMS Glendower, a 42-gun frigate, arrived in Gibraltar carrying 200 convicts to undertake the new defensive construction projects. Work began with the realignment of the new Line Wall from Prince Albert’s Front to South Bastion. Construction of the Defensible and Bombproof Barracks at Europa followed in 1845, and the project was completed by 1847.

The barracks block is built from locally quarried white limestone and rises two storeys above a basement. Its exterior presents a bold yet simple design, with each bay featuring a single arched window on the ground floor and two plain rectangular windows on the first floor.

In the late 1860s armament records show that the Retrenchment was armed with five 8-inch howitzers, and in addition, there were three 68-pounder guns, three 7-inch RBLs (Rifled Breech Loaders), and six 8-inch smoothbore guns in the area, possibly awaiting mounting.

In December 1872, it was reported that two 9-inch RML (Rifled Muzzle Loading) guns were ready to be installed, with only the carriages and platforms still awaited. It is likely that these guns were intended for the Buffadero positions rather than to reinforce the Retrenchment Block.

The site served as the Headquarters of the infantry battalion stationed in Gibraltar after WWII. During the construction of Lathbury Barracks in the 1960s, several window openings were cut into the wall, but otherwise, the work remains remarkably well preserved. It stands as the best-kept piece of fortification in Gibraltar and serves as a fitting memorial to the work of Sir John Jones.

Retrenchment Blocck inner courtyard.

Entrance to spiral staircase on left flank.

Exit for the spiral staircase on left flank.

Left flank couvre-port archways.