Its walls are fashioned out of fieldstone , laid dry in irregular courses .
It is a roughly square stone structure , its sides measuring between 36 feet 8 inches ( 11.18 m ) and 37 feet 10 inches ( 11.53 m ) in length .
structure 's walls are fashioned out of fieldstone , laid dry in irregular courses .
It is a roughly square stone structure , its sides measuring between 36 feet 8 inches ( 11.18 m ) and 37 feet 10 inches ( 11.53 m ) in length .