This rural complex is composed of a mediaeval chapel and a number of rooms, parts of which are rock-cut together with an artesian well and communal oven room.

The complex, including the chapel known as Santa Marija ta' Callus and the surrounding fields and orchards are mentioned in an inventory of the Order of St John when the Assemblea confiscated this property from Josefi Callus who was charged and executed for high treason against the Grand Master. The church consists of a small cubic room with three pointed arches and other mediaeval period church architectural features. A donkey-driven flour mill (mithna tal-miexi) was located within an adjacent large cave which cave is still existent, but without the equipment.

The complex was Malta's case site in an EU-funded project call Aramis (1998-2000) through which the mediaeval complex was restored and rehabilitated by the Restoration Unit and Mepa.

The project's publication included academic contributions as well as a section about the conservation interventions on this site. Arab-period influences are evident by rural water management features. Is-Simblija is at a short distance from Ta' Baldu where Roman remains are present.

Mepa scheduled the complex at is-Simblija as Grade 2 and Class B national monuments as per Government Notice no. 492/068 in the Government Gazette dated June 6, 2006.