1*72 A TOUR ROUND NORTH WALES. 



enemy, but from their length and nar~ 

 rownefs it is impoffible that this mould 

 ever have been the cafe. Others have 

 thought that they might have been left in 

 the walls to admit air, in order to harden the 

 liquid cement that was poured in ; but 

 this cannot have been fo, fince there are 

 fuch at Salifbury that appear to have been 

 clofed with {tone at the ends, and others 

 have been found even below the natural 

 furface of the ground at Manchefter. Mr. 

 Whitaker,* in his hifbry of Manchefter, 

 fays, that he by chance met with one that 

 was accidentally laid open from end to end, 

 which he thought difclofed the defign of 

 all the reft, and which he fuppofes to have 

 been this : that as the Romans carried their 

 ramparts upwards, they took off from the 

 prefTure of the parts below, and gave a 

 greater ftrength to the whole by turning 



* Second edition, vol. I. p. 47. 



little 



