Numismatically, Charles I's reign is without doubt the most interesting and complicated of any English monarch. Many varieties were produced at the Tower mint, and a number of provincial mints were opened during the Civil War, though as these were mainly opened to produce coins to pay the troops, the number of pennies produced there was quite low, as larger denominations were preferred. Between 1630 and 1639 the Frenchman, Nicholas Briot produced a milled coinage which for the first time included pennies. The quality of Briot's coins is superb, and one can only conclude that the only reason the Tower mint was not turned over completely to machine production was professional jealousy from the other workers.