^8 Memoir on the Aden JResenoirs. [no. 3, new series, 
Lord Valentia and Mr. Salt, regarding the origin of the tanks on 
the Islands of Dhalak and Kutto. 
Colonel Chesney mentions the fact of similar reservoirs un- 
doubtedly of Saracenic origin, existing in Granada, Cordova, Seville 
and Gibraltar, these, from the perfection of their coating, continue 
to be water-tight, though some of them, a^ those under the Castle 
of Gibraltar, must have been in use upwards of seven centuries. 
Two very remarkable cisterns exist in the ancient fortress on the 
summit of mount Agatha, in the Termino of Mercadel, in the Island 
of Minorca, the Moorish origin of which is attested- by an Arabic 
inscription. These differ from those of Gibraltar, by being raised 
structures instead of excavations, and they are of much greater di- 
mensions, being capable of containing 2173 tuns, or upwards of 
half a million gallons of water. 
Numerous other instances might be cited, but with the single 
exception of the great dam of Mareb, none equal the magnificent 
series lately discovered at Aden, which, when restored, will proba- 
bly contain not less than twenty or thirty million imperial gallons. 
There is no certain record of the construction of the Aden reser- 
voirs, and the natives of the place have no tradition regarding them 
in which they place much confidence. It is probable that some 
are of great antiquity, and that others were built as the necessity 
for them arose, or as the piety of individuals prompted them to con- 
struct some work, by which a great public benefit might be con- 
ferred upon their city. This latter supposition is supported by the 
fact, that under the domed entrance to one of them lately restored, 
a tomb, probably that of the founder, was discovered, and I have 
been given to understand that an inscription was removed from 
this tank by the late Surgeon Malcolmsbn, which probably would 
have afforded some clue to its history. 
My impression is, that the construction of these reservoirs was 
first commenced after the second Persian invasion of Yemen, about 
A. D. 600, but of this fact we have no authentic record. 
It is related by the Imam AH ibn Hoosain-el-Khuzraji, that 
Melek-el-Mansoor Taj-ed-Din Abd-el-Wahub ibn Tahir, sovereign 
