▁the ▁Lib urn ian ▁era . ▁Notable ▁examples ▁include ▁the ▁island ▁of ▁Bal jen ac , ▁which ▁has ▁ ▁of ▁dry ▁stone ▁walls ▁despite ▁being ▁only ▁ ▁in ▁area , ▁and ▁the ▁v ine y ards ▁of ▁Pr imo š ten . ▁ ▁In ▁Peru ▁in ▁the ▁ 1 5 th ▁century ▁AD , ▁the ▁In ca ▁made ▁use ▁of ▁otherwise ▁unus able ▁s lop es ▁by ▁building ▁dry ▁stone ▁walls ▁to ▁create ▁terra ces . ▁They ▁also ▁employed ▁this ▁mode ▁of ▁construction ▁for ▁fre est and ing ▁walls . ▁Their ▁as hl ar ▁type ▁construction ▁in ▁Mach u ▁Pic ch u ▁uses ▁the ▁classic ▁In ca ▁architect ural ▁style ▁of ▁pol ished ▁dry ▁stone ▁walls ▁of ▁regular ▁shape . ▁The ▁Inc as ▁were ▁master s ▁of ▁this ▁technique , ▁in ▁which ▁blocks ▁of ▁stone ▁are ▁cut ▁to ▁fit ▁together ▁tight ly ▁without ▁mort ar . ▁Many ▁j unction s ▁are ▁so ▁perfect ▁that ▁not ▁even ▁a ▁kn ife ▁fits ▁between ▁the ▁stones . ▁The ▁structures ▁have ▁pers isted ▁in ▁the ▁high ▁earth qu ake ▁region ▁because ▁of ▁the ▁flex ibility ▁of ▁the ▁walls , ▁and ▁because ▁in ▁their ▁double ▁wall ▁architecture , ▁the ▁two ▁port ions ▁of ▁the ▁walls ▁incl ine ▁into ▁each ▁other . ▁ ▁Const ruction ▁▁ ▁A ▁wall ' s ▁style ▁and ▁method ▁of ▁construction ▁will ▁vary , ▁depending ▁on ▁the ▁type ▁of ▁stone ▁available , ▁its ▁intended ▁use ▁and ▁local ▁tradition . ▁Most ▁older ▁walls ▁are ▁constructed ▁from ▁stones ▁and ▁b ould ers ▁cleared ▁from ▁the ▁fields ▁during