The People of Gibraltar
1771 - Thomas James - Herculean Straits - The Inquisition

From The History of the Herculean Straits Vol.1   (1771 - Thomas James)

Where were these ruins?

Probably the only question that can be asked about this enigmatic complex that can be answered with any degree of confidence - even though the very first mention of it in 1749 by Robert Poole in his The Beneficent Bee published in 1749 is quite ambiguous.
From hence we climbed up the Rock . . . which . . . was pretty much upon a level for a large field, though very rocky. .  Passing on we came to an old ruined place in the field, with divers cells underground. This was said formerly to have been the inquisition house, or place of punishment to the monastery. . 
Col. Thomas James writing in 1771 is somewhat clearer:
On the plain called upper Europa are the ruins of a house commonly called the Inquisition which name is acquired by the English, being raised close to the ruins of a circular building:
By “upper Europa” Thomas is referring to Windmill Hill. This is confirmed by the plan below in which the ruin captioned "g" is identified as a structure “called the Inquisition”.

A Survey of that part of Gibraltar called Wind-Mill-Hill    
(1777  - William Green Chief Engineer)

The plan suggest that it stood on an outcrop close to a cliff overlooking “the road to Europa” - Europa Road. 

Ten years later John Drinkwater in his History of the Great Siege confirms that it was still there:
 . . . at the southward, ruins of Moorish buildings are discernible on Windmill hill, and at Europa. The former are situated on an eminence. . 
An 1831 map of Gibraltar suggests that this “eminence” overlooked Europa Bay.

Map of Gibraltar showing a “tomb” on Wind Mill Hilll   
(1831 - W. H. Smythe)

What did the ruin look like?

Even without including his plan, by far the best description comes from Col Thomas James .
. . . a circular building; round the outside of which, are the remains of several apartments, three of them which are arched are entire, the rest can only be traced by their foundations. But by an old plan (which I saw) this ruin had a superstructure though no remains are now to be seen. . . .  
Whatever was the design of this building, it is very certain that the ends of those cellars were clothed with thick masonry, some of which the English soldiers broke through, in the hope of finding hidden treasure.
Not mentioned by Thomas are the square and rectangular objects shown on Green’s plan apparently lying on top of the circular structure. I hesitate to speculate as to what these were.

What was the complex used for?

There have been quite a few suggestions.
 . . . place of punishment to the monastery (Robert Poole 1749)
. . . some imagine it to have been a prison, and these cellars or vaults designed for criminals who were put in at one end that was afterwards closed up;  there to end their miserable days (or rather nights) by famine, erected at the commencement of the awful tribunal of the inquisition; while others ( and I think with more reason) imagine that it was a repository for the dead and that the centre was a sepulchre for the king, and those vaults for his children and relations.. . . 
It is said that don Henry was drowned, with forty of his knights in one thousand four hundred and thirty five and that he was buried in the upper part of the tower in the upper castle; but this is impossible because the tower was the residence of the King of the moors, and a mosque  . .  they never did  . . suffer a Christian to be buried near their place of worship. I therefore believe Henry's tomb was in this place and that it became a royal repository; but this is conjecture. (all by Thomas James 1771) 
Thomas’s “Henry” was Enrique Pérez de Guzman, the 2nd Duke of Niebla. He is supposed to have drowned together with a number of his followers while attempting to recover Gibraltar. The legend of what happened next, however, does not include any “royal” burial. Apparently his enemies recovered Enrique's body, decapitated it, and hung it inside a wicker basket on top of one of the towers on either side of the Puerta de la Barcina making the basket and its contents visible to any passing ship ,- where it hung for decades.

George Palao, a local historian came up with a new suggestion - the complex was a Phoenician Meghazil or funerary monument and the smaller building was an oratory or chapel.

(1978 - George Palao)

Could the complex have been the ruins of Torre de los Genoveses?

One of the oddities that make any discussion of the Inquisition complex particularly frustrating is that it is not mentioned by Gibraltar’s very first general historian - Alonso Hernandez del Portillo who wrote his Historia of Gibraltar in the 1620s.

Portillo goes out of his way to describe just about every other nook and cranny on Windmill Hill including the equally enigmatic Genoese Tower which no longer exists. This is how Portillo described it:
En este Tarfe (the area which today encompased Windmill Hill and Europa flats) esta una torre antiquísima dicha ahora de los Genoveses. No se sabe porque se le dio este nombre; a lo que de ella se pude conjeturar es que por estar esta torre en correspondencia de otra que ests fuera de esta ciudad casi de la misma fabricación de ella en lo alto de la sierra de la Carbonera, la  debieron de hacer los Cartaginenses o Romanos . . . . Tiene esta torre de los Genoveses al pie de ella un aljibe de agua antiquísimo, y con serlo tanto tiene todavía aquí. De la torre por su antigüedad esta  parte caída.

Tower at the top of Sierra Carbonera sporting signalling masts on either side  ( 1785 - Detail - Roberts)

The same circular Sierra Carbonera Tower in the early 20th century

Modern research suggests that the tower in Windmill Hill was part of a Genoese community who traded with the Moorish rulers of Gibraltar during the 14th century. The smaller building identified by Thomas in his plan as “the inquisition” fits nicely with Portillo’s “aljibe” - or cistern - in which case the round section of the complex could well have been one and the same as the ruins of the Genoese Tower.

Top - Section of plan in which the torre de los  Ginobeses equates with Torre de los Genoveses (1608 - Cristóbal Rojas)
Bottom Section of plan in which the Genoese Tower is labelled “h”. (1627 - Luis Bravo de Acuña)

As with Portillo other sites are mentioned in both maps but not the “Inquisition” complex. Although the Genoese tower appears in the right place in the top map, it seems rather too far to the east in the bottom one. This however, might be a question of the kind of perspective used by the cartographer.

Personally I believe that the two structures are indeed one and the same. In this I suspect I am in good company. Robert Poole’s 1749 comments on the Inquisition included the following:
This was said formerly to have been the inquisition house, or place of punishment to the monastery.
Tito Benady in his notes on the above in an article on Poole:
This is pure invention. Poole is describing the ruins of  the Torre de los Genoveses which was probably a depot for Genoese merchants in Moorish times and may have been built in the 14th or 15th century. 
Yes Sir. I agree.

See also:

1771 - Thomas James - Herculean Straits - Gibraltar
1771 - Thomas James - Herculean Straits - The Engravings
1771 - Thomas James - Herculean Straits - The Engravers
1771 - Thomas James - Herculean Straits - A Map of Gibraltar
1771 - Thomas James - Herculean Straits - Two Inscriptions