The People of Gibraltar
1704 - The Devil’s Mouth - La Boca de Fuego

R. Stewart Patterson (see LINK) in an 1884 article on Gibraltar - Topographia Infernalis  - which appeared in Notes and Queries for Literary Men makes a distinction between the entire Old Mole which he calls the Devil’s Tongue (la Lengua del Diabolo) (sic)and its battery – the Devil’s Tongue Battery (La Boca del Diabolo) (sic). He also offers an alternative name for the Mole – the Devil’s Mouth.
The Devil's Tongue (La Lengua del Diabolo) the point or spit of ground on which the Old 
Mole Battery is built. . . 
The Devil's Mouth.  (La Boca del Diabolo) was applied by the Spaniards to the Old Mole Battery, whose fire caused them much annoyance when they were besieging the fortress.

The Devil’s Tongue Battery occupying the top section of the Old Mole - the top bottom section seems to have been reserved for the storage of cannonballs   ( Late 19th century – G. W. Wilson ) (See LINK

It seems likely, however, that Patterson was mistaken as regards the name Devil’s Mouth. According to John Drinkwater (see LINK) writing about the Great Siege: (See LINK):
. . . . the ordnance in the lines, upon the Grand battery, and the Old mole, all together, exhibit so formidable an appearance to a spectator on the causeway, that the entrance into the garrison is called by the Spaniards, the Mouth of Fire.

Grand Battery on the left and the Old Mole on the right) "all together" perceived by Drinkwater to be a "Mouth of Fire"    ( 1740 - Williams from Skinner ) (See LINK

In other words Patterson was probably doubly mistaken - the Devil’s Tongue Battery was not called La Boca del Diablo - or even Diabolo and he also seems to have confused the legitimate Mouth of Fire (Boca de Fuego) with the nonexistent Devil’s Mouth (Boca del Diablo).  

The curved road in the centre of the photograph led to Landport Gate, the entrance into the town - A huge array of batteries would have had to be faced by any would-be invader – hence la Boca de Fuego  ( Late 19th century – G. W. Wilson )