▁following ▁a ▁pag an ▁pill aged ▁the ▁city ▁of ▁S igt una , ▁and ▁as ▁there ▁was ▁an ▁" E ar l " ▁named ▁Bir ger ▁around ▁at ▁that ▁time ▁too , ▁the ▁disput ed ▁origin ▁of ▁the ▁city ▁are ▁likely ▁to ▁remain ▁obsc ure ▁and ▁some ▁histor ians ▁choose ▁a ▁diplom atic ▁interpretation ▁saying ▁there ▁was ▁some ▁sort ▁of ▁fort ification ▁around ▁by ▁the ▁mouth ▁of ▁Lake ▁M ä lar en ▁when ▁the ▁city ▁was ▁founded ▁during ▁the ▁second ▁half ▁of ▁the ▁ 1 3 th ▁century . ▁ ▁As ▁S nor ri ▁mentions ▁no ▁city ▁in ▁his ▁account ▁but ▁some ▁sort ▁of ▁fort ification ▁called ▁a ▁k ast ali ▁( in ▁various ▁manuscript s ▁curious ly ▁said ▁to ▁be ▁located ▁east ▁and ▁west ▁of ▁Sto cks und ), ▁it ▁has ▁generally ▁been ▁assumed ▁this ▁fort ification ▁eventually ▁developed ▁into ▁the ▁castle ▁Tre ▁K ron or ▁located ▁where ▁still ▁is ▁the ▁Stockholm ▁Palace . ▁ ▁While ▁the ▁reli ability ▁of ▁these ▁stories ▁remains ▁disput ed , ▁d end ro chron ological ▁exam in ations ▁of ▁logs ▁driven ▁into ▁the ▁se ab ed ▁in ▁Nor r ström , ▁square ▁o ak ▁logs , ▁and ▁sun ken ▁logs ▁found ▁on ▁Hel ge and sh ol men ▁just ▁north ▁of ▁Stad sh ol men ▁in ▁ 1 9 7 8 - 1 9 8 0 , ▁concluded ▁these ▁trees ▁were ▁cut ▁down ▁during ▁the ▁period ▁ 9 7 0 - 1 0 2 0 , ▁most ▁of ▁them ▁from ▁around ▁ 1 0 1 0