usted ▁to ▁a ▁Spanish ▁architect , ▁Pedro ▁Luis ▁Es criv à , ▁an ▁expert ▁of ▁fire ar ms , ▁who ▁had ▁begun ▁to ▁build ▁Cast el ▁Sant ' El mo ▁in ▁Nap les . ▁The ▁discovery ▁of ▁gun pow der ▁obliged ▁to ▁new ▁methods ▁of ▁def ensive ▁construction . ▁Es criv à ▁was ▁in ▁charge ▁of ▁the ▁project ▁for ▁ 2 ▁years , ▁leaving ▁the ▁task ▁to ▁Gian ▁Gi rol amo ▁Es cri b à . ▁▁ ▁In ▁the ▁following ▁ 3 0 ▁years ▁the ▁heavy ▁tax es ▁necessary ▁to ▁build ▁the ▁for tr ess ▁imp over ished ▁the ▁city , ▁which ▁in ▁ 1 5 6 7 ▁begg ed ▁the ▁Sp ani ards ▁to ▁stop ▁the ▁construction ; ▁the ▁Royal ▁Court ▁granted ▁the ▁request , ▁and ▁works ▁were ▁interrupted , ▁so ▁parts ▁of ▁the ▁castle ▁were ▁never ▁completed . ▁The ▁for tr ess ▁had ▁cost ▁an ▁enorm ous ▁sum ▁for ▁the ▁times , ▁and ▁Aqu ila ▁was ▁obliged ▁also ▁to ▁sell ▁the ▁thick ▁silver ▁case ▁containing ▁the ▁body ▁of ▁St . ▁Bernard ino ▁of ▁S ien a . ▁▁ ▁The ▁for tr ess , ▁which ▁had ▁been ▁built ▁not ▁to ▁defend ▁the ▁city , ▁but ▁to ▁control ▁it ▁( its ▁can n ons ▁pointed ▁to ▁the ▁city ) ▁and ▁to ▁be ▁a ▁completely ▁self - su fficient ▁structure , ▁was ▁never ▁used ▁in ▁a ▁battle . ▁ ▁Architecture ▁▁ ▁Es criv à ▁planned ▁a ▁giant ▁for tr ess , ▁made ▁of ▁four ▁bast ions ▁connected ▁through ▁ 6 0 ▁meters ▁long ▁walls