Excavating a cave near the sacred Galilean catacomb of Beth She’Arim in 1956, a bulldozer unearthed an enormous rectangular slab, 11 × 6.5 × 1.5 feet. Rather than try to move the 9-ton mass, workers at first paved over it. Seven years would pass before anyone thought to examine it closely.

It was one gigantic piece of glass.

No one knows who made it or precisely how. Evidently an ancient furnace had produced great batches of molten glass that could be cooled and broken into reworkable pieces. This batch had been abandoned, perhaps because contamination had ruined its clarity.

Whatever its origins, it’s an amazing achievement. On its discovery, the Beth She’Arim slab was the third largest piece of glass ever made; even today, only large telescope mirrors rival its size. And it was produced 1600 years ago.