South Bastion was originally the Bastion of Senora del Rosario and was built between 1534 and 1535. The work on this bastion, and also Flat Bastion, was not completed at this time. In 1757 the British built twelve embrasures for guns facing due South. Two further embrasures faced out to the west over the harbour.
1856 returns show the following armaments for South Bastion, the carronades presumably in the casemated position covering Southport Gate.
- Twelver 32-pdr
- Six 8-inch
- One 10-inch Howitzer
- One 8-inch Howitzer
- Four 32-pdr Carronade
- One 10-inch Mortar
Between December 1880 and October 1881, a new battery of three 10-inch RML guns was built facing west over Gibraltar Bay. The guns were in Casemates behind iron shields, similar to those in Orange Bastion and Montague Bastion. Unfortunately this battery has now been built over and lost.
The other 10-inch RML gun batteries in Gibraltar are:
- Engineer Battery, 1 gun
- King’s Bastion, 4 guns
- Montague Bastion,3 guns
- Orange Bastion, 2 guns
- Parson’s Lode (Rosia No.9), 3 guns
- South Bastion, 3 guns
Bomb Proof Water Plant Located adjacent to South Bastion.
Water was a constant problem for the garrison of the Fortress in a time of siege, hence the building of the huge water catchment on the east face of the Rock.
The need to pump water at a time when the main motive power was steam meant the use of coal fired boilers. To produce steam, you need water and brackish water from wells were used for this. The steam produced once condensed provides a pure water. A progression was to use boilers purely for raising steam and condensing this steam in prepared condensers were the product could be run off to be used for augmenting the supply of drinking water. Very soon salt water was used as the source. The Sanitary Commissioners Water Supply Account for 1885 stated that half a million gallons of water were sold at 25 centimos per 15 gals (due to cost of fuel), whereas rainwater was sold at 22 centimos per 100 gals.
This bombproof water station was built about 1897. The water condenser was built in Silima, Malta where water supply was also a problem and they had built their own water plant. In 1897 there were also condensers at Rosia in an area leased from the Admiralty.