The valleys of the Aire and other rivers traverse it longitudinally, a fact to which its importance as a bulwark of north-eastern France is largely due.
Driven by Hill from Aire on the 2nd of March 1814, Soult retired by Vic Bigorre, where there was a combat (March 19), and Tarbes, where there was a severe action (March 20), to Toulouse behind the Garonne.
On the morrow of the marriage Louis, afterwards Louis VIII., seized Aire and St Omer in right of his mother, Isabella, and on this account Ferdinand refused his feudal duty in the English expedition.
Lesser ranges, which are included in the Beirene system and vary in height from 2000 to 4000 ft., are the Mesas, between the rivers Coa and Zezere; the Guardunha and Moradal, separating the Zezere from the Ponsul and Ocreza, tributaries of the Tagus; the Serra do Aire, and various ridges which stretch south-westward as far as the mountains of Cintra (q.v.).
The South Tyne and Irthing valleys cut off the Cheviots on the north from the Crossfell section, which is also marked off on the south by the valleys of the Aire and Ribble from the Kinder Scout or Peak section.
