This appears to be part of the original western ashlar boundary wall of the complex. The blocks of this N-S wall interlock with the E-W wall 5886, suggesting that there is an original corner preserved at the northern extent of 5908. There is also a physical relationship with the rectangular ashlar feature 5885 of uncertain function in the northwest corner of Room 20. At its southern limit, within Room 21, this wall appears to have been at least partially dismantled, spoliated, and subsequently rebuilt - partly in ashlars, and partly in opus reticulatum. The extant southern limit of the original wall is difficult to determine, as it is obscured by later constructions and unexcavated features.