[redhead]

"They melted it down and made it into money, odds are."

This was the first idea that crossed my mind, also. They would probably have done this for several reasons, over and above the need for more coinage. Mainly, I believe they wanted to teach the Jews a "lesson."

[TheAngryClam]

If burning the whole country down, breaking out the salt for the fields, deporting a whole mess of them, enslaving tons more, and publicly executing any leaders they could get their hands on (apart from Josephus), wasn't enough.

[LN2Campy]

even if the Romans didn't melt it down, the Goths who sacked Rome in 410 AD more than likely did so-- not to mention the mideval Roman "nobility", who, in constructing their villas and palaces, treated the classical structures of Imperial Rome as rock quarries, going so far as to burn marble statues to make lime for mortar.