Fort Mosta

Few British-period works of military architecture manage to exert such a commanding presence,

as well as a sense of solidity and domineering invincibility, as Fort Mosta (or Musta as it was officially referred to by the British military).


Occupying a central position along the escarpment of the Great Fault, Fort Mosta was the most strategically-placed land fort on the system of inland defences known collectively as the Victoria Lines.  The Fort’s designation as a ‘land fort’, its strategic location roughly in the centre of the North-West front (later renamed the Victoria Lines), and the topography of the site on which it was built, were all to dictate both its structural shape and form and its defensive role (and, hence the nature of its armaments with which it was to be equipped).


Today, this important example of late nineteenth-century British military architecture is currently used by the Armed Forces of Malta as a storage depot. It state of preservation, despite the Army’s many effort to keep it in good condition, is such that it requires, and deserves, specialized attention and interventions to counter the damage that is being inflicted to the structure as a result of the particular geological conditions of the site.  Furthermore, a military architecture entity of such calibre, effectively a strategic nodal point in the extensive system of fortification known as the Victoria Lines, deserves to be integrated more productively into the broader cultural and tourism sectors for the greater common good.



A Nodal Land Fort on the North West Front


Fort Mosta was originally designed as one of three isolated strongholds on the North-West Front.  This was a defensive position adopted by the British military and intended to divide Malta into two parts, concentrating the fortified assets along the line of a natural fault cutting across the width of the island - for more information go to our article. Fort Mosta’s construction was approved in I873, but, in actual fact, the first of these strongholds to be initiated was Fort Bingemma, begun in I875. This was then followed by Fort Madalena in I878, and by the time of General Lintorn Simmons’ visit to Malta in February I878, work on Fort Mosta had not yet commenced.


Simmons visit, however, seems to have put the wheels in motion for the construction of the structure was commenced some time after. The new work of fortification, designed as a hill fort, came to consist of two main component parts – a casemated keep of pentagonal plan, surrounded by a defended ditch, and an external battery. Owing to the fact that no initial, or even period, record plans of the fort have survived, it is difficult for historians of British military architecture in Malta to determine the configuration of the original design, particularly where it involved the annexed battery. The present structure provides various hints of an incremental development. The addition of two disappearing gun emplacements in the 1890s, for example, would have witnessed the replacement of earlier barbette emplacements (as is known, and documented, to have happened at Fort Bingemma).


Ancient Strategic Site


Fort Mosta occupied the cliff face on the spur of land at the mouth of Wied il-Ghasel and was apparently built (according to available documentation and some archaeological evidence) on the site of a Bronze Age citadel and village which was recorded by George Grognet de Vasse (1773-1862), a French Architect resident in Mosta who designed and built the Rotunda church of St Marija Assunta in Mosta. If any such remains had existed at all (and this is debatable) the British military certainly showed no concern for the antiquity of the site, and simply requisitioned the whole area for defence purposes.


Like most of the forts of this period, late in the history of fortification, the design of Fort Mosta was tailored around its perceived role, and the armament considered suitable for the task. Initially, this was to consist of seven 64-pdr smooth-bore muzzle loading guns mounted inside protective vaulted casemates. Seven other guns proposed to be installed on disappearing carriages were, however, never mounted. Presumably these were to be mounted within the outer battery.  Two other casemates, conceived and built in Haxo style, were situated on the west side of the outer enceinte and were designed to enfilade that part of the escarpment overlooking Targa Battery.


gun embrasures opening from the casemates, had serrated cheeks and surfaces, designed to help deflect incoming cannon shot, while buttresses on the east north east face acted as traverses.  Unlike most of its sister defences, Fort Mosta was not intended to be armed with the heavy RML guns, mainly because it was conceived primarily as an inland fort with no coastal defence role.

Aerial view of the keep of Fort Mosta, with the battery shown in the background to the rear, c.1970. (Image source: Courtesy of the Department of Information, Malta).

Detail of keep of Fort Mosta, showing exterior slope of earthen parapet with gateway and its small flanking musketry gallery (Image source: Author’s private collection).

The main entrance into Fort Mosta, situated in the south face of the keep and protected by an adjoining musketry gallery (Image source: Author’s private collection).


The Pentagonal Keep


Undeniable, the most structurally imposing and defining feature of Fort Mosta is its keep.  Like most other British forts from the period, it is not known who actually designed the structure. The Commanding Royal Engineers at the time was Col. T. Murrey, but more likely than not the whole design and construction process involved the whole engineering staff and cannot be attributed to any one individual.  The only two other contemporary forts that were given a polygonal type of keep were those of Bingemma (1875-78) and San Leonardo (1875-78). The latter bears some similarity in the form of its diamond-shape plan, and the shape of its parapets, but this lacks both the scale and the towering command of the Fort Mosta keep.  Furthermore the Fort Mosta keep is more than just a place-of-last-resort, as employed in the two earlier forts mentioned above. Indeed, considering its comparatively large size and its many casemated gun emplacements, the keep at Fort Mosta can easily pass off as a veritable fortress in its own right. In this regard, its design may, as a matter of fact, have been directly influenced by the plan of Fort Tombrell, a hexagonal work of fortification (shown below) which was proposed for the defence of the Delimara peninsula in the south of Malta but never built, its place eventually taken by another larger land fort, Fort Tas-Silg built in 1879-83 (a special article on Fort Tombrell is scheduled to be featured on MilitaryArchitecture.com in the coming months). Therefore, rather than being simply a keep, the structure was actually the original fort and only became a ‘keep’ at a later stage in the design process when the outer detached ward, or battery, was thought necessary and grafted onto the position to give it its present shape. Further research, however, is necessary before any conclusions can be drawn on this matter.


Plan of keep of Fort Mosta at casemate level, showing gun emplacements, magazine and sally-port leading down to ditch. (Image source: Author’s private collection).

Basement level plan of the proposed Fort Tombrell, dated 1872. Note the counterscarp musketry galleries. This proposed fort was designed to be armed with six 64-pdr guns on Moncrieff disappearing carriages and three 11-inch RML for coastal defence (Image source: Author’s private collection).

Detail of interior of keep, showing terrace and courtyard, with rear of main entrance (Image source: Author’s private collection).


The main defensive elements of the Fort Mosta keep were its enveloping ditch, which isolated the keep from the outer enceinte and also from the mainland to the rear, and three counterscarp musketry galleries which provided the necessary enfilading fire, and were linked to the keep by means of an underground tunnel. One of the counterscarp galleries occupies two faces of the counterscarp wall, creating, in effect, a total of four sets of firing positions, each containing a central embrasure for a 24-pdr S.B. B.L. carronade and six musketry loopholes.  All the galleries were protected, externally, by a shallow drop pit revetted in concrete. Entrance into the keep was through a main gateway situated in the middle of the south face and this led directly into a spacious central courtyard. The gate was served by a Guthrie rolling drawbridge, which hasn’t survived, and was flanked by a small defensive musketry position containing three loohpholes.

Detail of ditch enveloping the keep, showing one of the counterscarp galleries (Image source: Author’s private collection).

Detail of one of the counterscarp galleries flanking the ditch, showing the central embrasure for the 24-odr carronade (Image source: Author’s private collection).

Underground communication tunnel leading from keep to the counterscarp galleries (Image source: Author’s private collection).

Detail of musketry loophole in one of the counterscarp galleries (Image source: Author’s private collection).


A secondary gateway, more of a sally-port really, lead down into the ditch of the keep and was designed to provide communication between the keep and the adjoining battery. This may, in fact be a later addition, given that the masonry facade with its four adjoining loopholes, are fitted within a projecting concrete slab that buttresses the whole west side of the keep. The secondary gate was served by what appears to have been a chain-and-tackle type of drawbridge.

Fortified sally-port opening into the ditch along the west side of the keep. This was served by a drawbridge of unknown configuration (Image source: Author’s private collection).

One of the various fissures cutting through a buttress added to stiffen one side of the walls of the keep (Image source: Author’s private collection).


This heavy buttressing, as a matter of fact, is present throughout various parts of the forts and reveals that very early in its service, the original structure erected in 1878 had to be stiffened to counter the instability created by the largely clayish terrain on which the fort was built.


A walk through the ditch quickly reveals that, in some areas of the fort, the foundations were laid upon a thick concrete raft resting on a layer of clay.  According to Hyde, the fort was built over a very yielding layer of Blue Clay whilst the solid lower Coralline Limestone was so very near that it formed part of the adjoining ditches.  Indeed the fort bears many marks of structural instability as can be attested by the large number of buttresses reinforcing the revetment of both the keep and the outer battery.

External view of the embrasures for the Haxo-type casemates along the west side of the fort (Image source: Author’s private collection).

External view of one of the embrasures for the Haxo-type casemates along the west side of the fort (Image source: Author’s private collection).

View of the rear of one of the two Haxo-type casemates along the west side of the fort (Image source: Author’s private collection).

View, from the keep, of the battery for two 6-inch BL guns on disappearing HP mountings (Image source: Author’s private collection).

Upgraded armament


In I866, it was recommended that two 6-inch breech loading guns be mounted within the fort, one on the western outerwork and the other on the site then occupied by the useless Haxo casemate (0’Callaghan & Clarke, I886). The two 64-pdrs in the right casemates overlooking Madliena were proposed to be replaced by two 6-pdr QF guns, while the counterscarp flanking galleries were to be armed with 32-pdr SB, B.L. guns.

View of the 24-pdr carronade on cast-iron garrison carriage, placed inside one of the counterscarp galleries defending the ditch of the keep of Fort Mosta. This gun was originally located on Despuig Bastion at Mdina (to the rear of the cathedral), and was generously transferred to Fort Mosta (via the then NTOM) by the Cathedral Chapter during the mid-1990s (Image source: Author’s private collection).


Despite these alterations, Generals Nicholson and Goodenough, in 1888, remarked that Fort Mosta was not a satisfactory defensive work for the important strategic position that it occupied:


“Fort Musta is not a satisfactory work, but the position is a commanding one, and when re-armed, as proposed, it will fulfil its object. It would not be worthwhile to incur the expense of reconstructing it. We think that the 5- 32pr. S.B.  B.L. guns proposed to be supplied for flanking ditches might be omitted, and 3-pr. Q.F. guns on field carriages substituted for 6-prs’


However, it would seem that the counterscarp galleries never received their smooth-bore 32-pdr breech loading guns. Two gun emplacements for 6-inch BL guns on hydro-pneumatic disappearing carriages, on the other hand, were constructed on the outer ward of the fort accompanied by their underground magazines, stores, and guncrew shelters.

Above, diagram showing a 6-inch BL gun on hydro-pneumatic disappearing mounting with its protective overhead ‘turtle-back’ type of cover designed to shield the guncrew from aerial bursts. Also shown are various surviving examples of the 6-inch BL gun and its mounting found in various forts around the world (Image sources: Author’s private collection).

Detail of concrete aggregate as found on the revetment of the keep and the counterscarp of the ditch (Image source: Author’s private collection).

Above, A typical section of smooth faced masonry finish found on the interior walls of the fort, most of which were constructed of soft Globigerina limestone (Tal-Franka ) and often whitewashed with a mixture of lime mortar and sand, traces of which can still be seen on the wall (Image source: Author’s private collection).

Construction Materials


Like most of the first-generation British forts of the 1870s, Fort Mosta was constructed from a hybrid combination of masonry, hewn rock, earth, and cast-in-place mass concrete elements.

The initial concrete was employed largely in the revetments along the scarp and counterscarp walls, and in the formation of a raft foundation over which various elements of the structure were built (in parts of the battery). The other elements which were built in concrete were the two gun emplacements for the 6-inch BL guns, but these were added later in the 1890s and use a more compact mixture. The casemated gun emplacements, vaults, gateway, and various underground magazines, on the other hand, were constructed in masonry and covered over with a thick layer of protective earth.

At Fort Mosta the original concrete was used un-reinforced and cast in lifts of approximately the same height. The concrete walls do not display any expansion joints although, in various places, and at somewhat irregular intervals, these are perforated with small rectangular holes, particularly at the horizontal interface of the concrete wall and the underlying masonry or bedrock. This seems to suggest that the openings served as weep-holes rather than as anchor points for formwork ties.  Most of the concrete revetments in the Malta fortifications from the 1880s, the revetments at Fort Mosta have lost their smooth cement surface finish (owing to deterioration), to reveal cast layers of hardstone aggregate of non-uniform grading. A significant proportion of this aggregate is quite elongated and the proportion of the aggregate appears rather low. Similar method of concrete construction can be found in the walls or ditch revetments of Fort Bingemma (1875), Fort San Leonardo (1878) and the Dwejra lines (1881) and the 100-ton gun batteries at Cambridge and Rinella.


An important element in the design of Fort Mosta comprises the thick earthen mounds which form the large parapets covering the keep and adjoining battery. This terreplein was formed from a rather coarse, dry mixture of stone chippings (varying considerably in size and often obtained during the excavation of the ditch), combined with earth and soil.  Along most of the revetments (except for two of the rear faces of the keep, the thick earthen parapets are revetted with a masonry skin of hardstone capstones laid in an inclined plane on the exterior slopes, a technique which was first employed in Malta on the Corradino Lines in 1872. Such a covering helped hold the earthen fill in place, and prevented it from being carried down into the ditch below by torrential downpours.

Where employed as a surface finish, particularly on the external elements of the fort’s walls, the masonry used was of the drafted type, with flat bossing in low relief (known in Maltese as ’bunja’), creating an overall rusticated feel that was popular with the Royal Engineers and was employed in most military buildings of the period.  In most cases, the softer Globigerina Limestone was employed while a harder quality stone, the Coralline Limestone, greyish-white in colour, was often employed in capstones of the exterior slopes of revetments and in various secondary features. Amongst those features built in hardstone one finds the revetted cheeks of the embrasures of the Haxo-type casemates and its rear walls, and the various buttresses which were added to stiffen various parts of the enceinte.



Change of Role


With the abandonment of the Victoria Lines as an inland defensive position during the early

years of the 20th century, Fort Mosta lost most of its military value, unlike the other two forts on the Victoria Lines, which were retained in use in a coastal defence role. By 1940, the fort was being used simply as a munitions depot, a role which it has continued to fulfil up to the present day.

Dr. Stephen C Spiteri PhD  - MilitaryArchitecture.com (C) 2011


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