I'm the lead archaeologist on two Spanish Mission projects in California and at one of them we discovered lime mortared "tanks" in one of the quadrangle wings. They measure 3 m x 0.8 x 0.84 m in size. The top of the "tank" is at the interior surface grade. We have been unable to identify the function of these features and do not believe that they are products of some post-Spanish activity. One of the docents at the site thought they may be part of rain water catchment systems. I understand that these same features may be present at Pompeii and would greatly appreciate being directed to someone or sources that may help our understanding of these features.
John M. Foster, RPA