It is a rectangular smooth piece of stone 25x23x4cm incised on the top with 5 crosses. This stone carried the bishop's blessing. The style of the crosses suggests that this portable altar dates from the 13th C.

This would have been used by the Prior as he moved around Coldinghamshire. When he came to a chapel which had not been visited by a bishop and so its altar had never received the bishop's blessing, then by placing the portable altar on the unblessed altar the latter became fully functional.

It is more clear on some of the incised 5 crosses than others, but each carries the 5 points of the cross (this is clearest on the top right cross). These points refer to the 5 nail holes (stigmata) in the body of the crucified Christ.