The birth of the Christian Altar
During a visit to Syria in 2003, we visited the Church of Saint Sergius at Maaloula.
Entrance to the Church of St Sergius
Here are to be found some of the earliest altars, known in the Christian Church. To quote text from the
Mar Sarkis Monastery website : "
Now, in 313 A.D. with Constantine the Great, the church began to think how to have its own ecclesiastical architecture to make more difference between pagans and christians, that's why the first Council of Nicea, gathered in 325 A.D., decided not to build anymore altars with a pagan architecture but flat altars. This is the main proof that the church existed before this decision, before 325 A.D. "
The earliest is the main, central altar, which has a very characteristic shape, like an inflated capital D, or Sigma form, with one flat edge, and a curved end. This has a pronounced raised ridge round it's perimeter. This, was to prevent the spread of blood from sacrifices, in its earlier use by Jews (According to our guide, Abdallah Hadjar) or earlier Pagan Roman usage. It's position as central altar is based on it's inferred antiquity.

Main Altar at St. Sergius, Maaloula, Syria

A close up of the top of the central altar, showing it's raised rim and overall shape,
with it's flat end facing the front.
In a side chapel. was to be found another early altar, again with a raised edge, but with a rectangular shape.

Another early, but rectangular altar, from St Sergious, again with a raised rim.
Forward to 2006 and a visit to Aquileia, Northern Italy. Here were to be found altars to match the Syrian forms. The first to be figured comes from the Paleo-christian Museum, Monastero, where it was un-officially photographed. It is the same shape as the Central altar at St Sergious, but differs by having a very decorated upper surface. This has been shaped into place settings, replicating the table setting for the Last Supper, but still retaining the raised rim. Interestingly enough it shows a break in the straight edge of the rim, in the same position as in the Syrian form. It has previously been described and figured in a populist guide books (G. Brumat Dellasorte, 2005, pp. 51-2, Fig. 80 & G.Brusin, 1966, Fig.23).

Early altar from the Museum of Paleo-christianity, Aquileia.

Enlarged detail of early altar from the Museum of Paleo-christianity, Aquileia.
Finally from the Maxentius Crypt of the Basilica more famous for it's frescos, comes a rectangular altar again with a raised rim.
In conclusion, all four altars follow a similar pattern of raised rim and are derived from earlier pagan forms. They fall into two groups, the 'D' shaped and rectangular, the former probably being the earlier. In any case it is likely that all four date stylistically prior to 325 A.D. and show the gradual process of change to the flat, rectangular altar slabs of later history!
Reference
G. Brumat Dellasorte, 2005. Aquileia and San Canzian, pp. 96, Figs. 150. Storti Edizione, Venezei
G. Brusin, 1966. Aquilleia a short guide. pp. 96. Figs. 55, 8 colour plates. Tipografia Antoniana, Padova.