The Mystery Slab

The town of Beit She’arim, in Galilee, has an important place in Jewish history. Founded during the reign of King Herod in the first century BC, Beit She’arim was a prosperous market town that became the de facto capital of Israel in AD 70, after the destruction of the Second Temple forced the Sanhedrin (the Jewish legislature and supreme council) to evacuate to Beit She’arim. The town was destroyed by fire during a rebellion in AD 352, and although it was resurrected by the Byzantines and later the Arabs, the town never regained its luster. In fact, it was a sleepy Arab village named Sheikh Bureik when it was purchased by the Jewish National Fund in the 1920s.

Beit She’arim was also the site of a large and important cemetery. Historically, the most desirable burial place for Jews was the Mount of Olives in Jerusalem. But once Jews were barred from the area in AD 135, Beit She’arim became the main alternate burial place. Jews from as far away as Tyre and Palmyra were buried there, as was Rabbi Judah HaNasi, the second century AD Jewish leader who codified Jewish oral tradition into the Mishnah, which itself became the basis for the Talmud. Needless to say, HaNasi is a really important guy in Jewish history.

Because of all this, archaeologists had studied the area around Beit She’arim as far back as the 1880s. By the 1950s, the area around the cemetery had been excavated so well that it was decided to build a museum on the site. And so, in 1956, a bulldozer was brought in to flatten a small, archaeologically insignificant cave. But shortly after the bulldozer went to work, it hit a gigantic item that it couldn’t move. The item – which was 6½’ x 11′ and 18″ thick – weighed 9 tons and was, strangely enough, perfectly level on top.

For whatever reason, people at the site didn’t seem all that interested in the find, and so paving stones were placed over the slab and construction on the museum continued. But scientists around the world were intrigued by the mystery, and so in 1963 a joint expedition of the University of Missouri and the Corning Museum of Glass decided to check out the slab, thinking it might be made out of glass. And, sure enough, it was.

It seems that ancient glassmaking was done in two stages – an “engineering” phase and a “design” phase. In the engineering phase, raw materials like sand and silica were heated to over 2000°F (1100°C) in giant furnaces until the mixture glowed white hot. Once these giant slabs were cooled, they became glass. These big slabs were then broken up into smaller pieces and sold to glassblowers all over the region. The glass blowers would then reheat the raw glass and shape or blow it into the final desired form (the “design” phase).

So it seems that there was once a huge glassmaking industry at Beit She’arim. But what amazed scientists was the sheer scale of the operation. Almost 11 tons of raw materials were required to make a slab of glass that big, and the logistical systems needed to make such a thing are still non-trivial today – to say nothing of 1600 years ago. For example, those 11 tons of raw materials would have to be held at 2000°F for 5-10 days, a feat that required 20 tons of fuel.

Many mysteries about the slab remain, but one thing is clear: the slab was left there because it was considered defective. Most glass of that era contains 8% lime, but this slab contains over 16% lime. This made the glass cloudy – which is why it was rejected back then and why there was initial confusion in the 1950s over what the slab actually was.

There’s one more amazing fact about the “mystery slab”: when it was identified as glass back in 1963, it was the third-largest piece of glass ever made! Only two large telescopes made before 1963 were larger than the slab, and even today only a handful of glass pieces – again for telescopes – are larger than the slab… which was made 1,600 years ago.

Read more about the Mystery Slab here.

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