Archaeologists usually recover their treasures beneath the earth. Instead of digging beneath the earth, however, we were high above it on a four-story scaffold, exploring the half-dome of the apse of the Byzantine Church at Saint Catherine’s monastery at the foot of Mount Sinai. But we felt as much like archaeologists as those who dig deep in the earth. For we too were recovering the past. We were reclaiming one of the world’s greatest Byzantine mosaics—from centuries of dirt, grime, varnish and even glue which had collected on its surface. Gradually, as the surface was painstakingly scraped with delicate dentists’ tools and then cleaned without chemicals, what had been dull, faint, discolored and often obscure emerged brilliant, clear and breathtaking, just as it must have looked more than 1400 years ago when artists and workmen created it at the command of Emperor Justinian I the Great (527–565).