The inherent difficulty of adequately lighting barrel vaulted structures has been widely acknowledged. The intrinsic engineering issue is the need to avoid fenestration punctures in stonework barrel vaults. Such openings could compromise the integrity of the entire arch system. Thus the Romanesque medieval builders had to resort to techniques of small windows, large buttresses, or other forms of interior wall cross-bracing to achieve the desired lighting outcomes. In many of the monasteries, a natural solution was cloisters which could have high barrel-vaulted construction with an open courtyard to allow ample lighting.