Finding a cross like this one has been a lot harder than I thought it would be. They called it a Chi Rho symbol. It's more like a Tau Rho, Monogrammatic Cross or a Staurogram. The Staurogram was first used to abbreviate the Greek word for cross in very early New Testament manuscripts. A Tau-Rho is a T-Tau with a P-Rho. Then the shape of the P, (the Rho) at the top of the Aluma Cross had me baffled. Looked Egyptian, looked like a oil lamp handle, or as Len posted a shepherds crook/staff.
The Aluma Cross shows the transition from a traditional Egypto-Roman Religion to Christianity. The cross displays traditional forms belonging to both religions. In my opinion making the cross Coptic/Egyptian-Christian. Unlike a Chi Rho, the X-shaped St. Andrew's cross has been replaced by a large Greek cross. The only remainder of the Rho is a small P-shaped "handle" at the top of the cross. The result is a Tau-Rho with strong resemblance and symbolic connection both to the Greek cross and to the ankh cross.
Indeed a tough one, not your standard form of cross. The photo below is from a 4th Century Coptic Christian "Codex Glazier". I think our Pheasants need to turn into Peacocks.

There's more than one reason for this, not just because of the below photo, but the Demetrius I'm concentrating on now has a lot to do with Easter. I need to have a talking to the artist of the Aluma mosaic! I'm not liking the leopard much either. The leopard looks like a calf with teeth. His Peacocks look like Pheasants. (giggle). Ok, so the artist was no Michelangelo, but it's a fantastic piece.
Ancient people believed that the flesh of a peafowl did not decay after death, and it so became a symbol of immortality. This symbolism was adopted by early Christianity, and thus many early Christian paintings and mosaics show the peacock. The peacock is still used in the Easter season especially in the east."
http://en.wikipedia.org/wiki/Christian_symbolism

The next photo is an Ancient Coptic Christian wall carving at the Temple Of Isis Philae near Aswan Egypt. Shows the presence of Copts from an earlier era in the Egyptian Region. I'm using it to show the shape of the ends of the cross, the 4 Points, (dots at positions North, South, East And West), the Shepherd Crooks, and the relationship to the Ankh.

The below photo is of Coptic funerary reliefs, (5th-6th century AD), that show the transition in Egypt from traditional Egypto-Roman religion to Christianity. Finally found the exact cross today, on a gravestone no less. In identifying Ra/Helios with Christ, one passes symbolically from pagan (Life in Ra) to Christian (Life in Christ) faith and belief. Look at the center cross.

Think it's safe to say Aluma is a Coptic=Egyptian Christian site?