War as was uncommon in the period and there is no evidence of it that I know of in Orkney . It appears that interpersonal violence was common for the period and here too , but you don't need big walls to put a stop to that or raiding which was more suited to mainland areas where you get in and out easily and quickly , not easily achieved on Orkney . The earliest defensive structures on Orkney look to be have been promontory forts and brochs ,both much later than the Ness .