Tower houses of this type were built across Connacht from roughly the fourteenth to the sixteenth centuries, typically by Gaelic Irish or Anglo-Norman lords as fortified residences, and Rappa is a particularly solid example of the form, its walls still rising to a considerable height above the surrounding farmland.

The castle is associated with the MacJordan family, a branch of the Norman de Jordans who became thoroughly Gaelicised after their arrival in Connacht. The MacJordans held territory in this part of Mayo for several centuries, and Rappa appears to have served as one of their principal seats. The structure follows the standard tower house plan, a tall rectangular block with thick walls, vaulted chambers at lower levels, and the remains of a bawn, the defensive enclosure of wall that would have surrounded the base of the tower to protect livestock and dependants in times of trouble. In the context of late medieval Mayo, where power shifted constantly between Gaelic lordships and outside pressures, a fortified bawn was a practical necessity rather than a display of status.