By minting their own coins they declared themselves independent and sovereign, no longer required to obey Roman laws in contravention of their own religious strictures.
The new shekels were dated from the start of the revolt, so the ones minted in 66 A.D. are inscribed “Year 1.” Moneyers struck a few prototypes first to figure out the design and mechanics of minting large silver coins. Two of those prototypes are known to exist, both struck from the same dies. They were discovered in the late 1970s. One of coins was donated to the Israel Museum in Jerusalem. The other just sold to an anonymous overseas collector for $1.1 million.
Above: these Tyre shekels were the model for the Jewish coins.