THORNY PLANTS NATURAL FORTIFICATIONS 127 



plantations of thorny plants, as to form a natural fortification 

 impregnable to the feeble tribes on the other side ; and at 

 each pass which led to the level country, movable gates, 

 formed of the same thorny beams, were suspended as an 

 aiirple security against the incursions of the naked and 

 timid lowlanders. 



