The Greek word translated by this phrase does not mean that the wall was totally jasper; instead, the term means that the wall (presumably of stone and masonry cement) was embedded with countless jaspers. The resulting message is that glorious God himself forms the wall around the Bride, the holy city, and so is her protector. This is very much the instruction of earlier Scripture (Deuteronomy 33:27; Psalm 18:2; Psalm 27:1; Psalm 48:13; Psalm 51:18; Psalm 122:7), and the reality for the church even today.
18 The wall was built of jasper, while the city was pure gold, like clear glass.