Double breasted or center fastening?

[Paullus Scipio]

Paul: surprisingly, out of the nearly 1,000 examples of warriors wearing this type of armor (your tube and yoke) on vase paintings, none of them are shown wearing a belt (like the one Alexander has on the Alexander mosaic). These belts only appear on Roman items and are pretty rare.

Strictly speaking, this item, worn around the ribs, and tied with "the knot of Hercules" ( reef knot), with the ends tucked in, is a girdle, not a belt ( 'zoma' in Greek).

It was supposedly a symbol of high command and is often seen worn over the 'muscled cuirass' on Imperial Roman statues and such-like. As you say, Alexander wears one over a Tube-and-Yoke corselet on the mosaic. Given the accuracy of detail shown on the mosaic, it is probably not an anachronism, and may have originated with him, and worn in imitation thereafter......