Fort Rinella will soon have the only operational retractable bridge of its kind in the world as part of a project launched by Fondazzjoni Wirt Artna which manages this 19th-century fortification.

Financed by the Eden Leisure Group, the €60,000 job will involve the construction of a replica of the fort’s original bridge using some of the original parts which will be restored.

Named after Charles T. Guthrie, the British engineer who had designed it in 1869, the bridge was one-of-a-kind as when not in use it would slide into the fortification.

Its advantage over traditional drawbridges was that when closed it would not obstruct the fort’s gate,  allowing better defence of this potential weak spot in case of attack.

Our objective is not to have an exact replica of the original bridge, but make it fully operational in order for visitors to have a complete experience. This will be the only such operational structure in the world- Mario Farrugia

Addressing a news conference, Mario Farrugia from Fondazzjoni Wirt Artna noted that parts of the mechanical structure had been found scattered in various parts of the fort - built between 1878 and 1886 - when they had taken over the site in 1991.

“Our objective is not to have an exact replica of the original bridge, but make it fully operational for visitors to have a complete experience. This will be the only such operational structure in the world,” he said.

A similar mechanism had been installed at Fort Cambridge in Sliema, and parts of it which were still in place until the late 1970s had been brought over by the foundation, with the intention of restoring it.   

Though information on the mechanical specifications of this structure was very scarce, Mr Farrugia pointed out that the restoration project became possible thanks to a historic document the FWA was handed over. It transpired that the standing orders of the Malta Garrison of 1897 contained the operational drill of the bridge.

Mr Farrugia demonstrating the mechanical operation of the Guthrie Bridge using a scale model. Photo: Jonathan Borg

“This enabled us to understand the scientific model and hence be able to recreate the mechanism thanks to new technology in collaboration with the University of Malta,” he said.

Mr Farrugia said this particular model was designed in such fashion to make it possible to export to British colonies as it could be easily assembled by an unskilled person.

These bridges, which could carry up to about three tonnes, started to be phased out in the 1920s as they could not support the weight of motorised vehicles and trucks.

In the case of Fort Rinella, the bridge was replaced by a masonry one in the 1930s. The latter was partially destroyed by enemy bombing in World War II.  The project is estimated to take one year to be completed.

Design of the bridge

The bridge consists of two parts: a rolling platform and a counter-weight mechanism supporting the bridge.

The counterweight mechanism consists of two iron counterweight arms fitted with trucks at their bottom end to slide on wall-mounted rails under the gate. The arms are held together by means of two metal crossbars which also act as distance pieces. The arms are hinged to the scarp wall under the gate.

The two counterweights weigh about half the weight of the platform which they are meant to propel and support. They are positioned in line with a projecting horizontal spigot on either side of the rolling platform which they are to catch into when the bridge is balanced on them in the act of retracting or extending.

The rolling platform is rectangular in shape. It is built from an iron joist frame covered with heavy wooden planks. Two metal roadways are attached to the planking as protection against the excessive wear caused by wagon traffic.

Similarly, two heavy wooden berms run longitudinally along the edge of the platform to stop wagon wheels from being trapped into the bridge iron railing. The platform has two iron trucks and a spigot on each side.

Mechanical operation

The retraction of the bridge required the attachment of a length of tackle to a metal loop half-way the platform to help pull the platform inside. A locking pin which kept the bridge secure was to be removed from inside the fort and the back end of the bridge was to be lifted clear from the ground.

This would set the retracting mechanism in motion and the bridge was pulled inside the fort using a block and tackle and rolled on the iron rails set in the entrance floor.

To roll the bridge out four soldiers were required to stand on the rear edge of the platform to weigh it down in the process of rolling it out. This would keep it in a steady horizontal position ensuring that the two projecting spigots positioned on either side of the platform are caught correctly by the two counterweight arms in the ditch which automatically rests the bridge into its place.

A cross-section drawing of a Guthrie Bridge. Photo: Fondazzjoni Wirt Artna

A computer generated imaged of the retracted Guthrie Bridge at Rinella. Photo: Fondazzjoni Wirt Artna

The mechanism used to support the retractable bridge

A side view of the Guthrie Bridge planned for Fort Rinella.