Currencies

[ANTONIVS MAGNVS]

So it was more profitable to melt the Denarii than actually using them as a currency.

That's what the Emperor did! He would order the high content silver denarii out of circulation and re-mint them with the new debased content. That is why pre-reform denarii of Nero are rarer than the post-reform denarii. Lower weight and lower silver content meant that you could circulate more coins with the same amount of silver. Of course it was difficult to recall coins from previous Emperor's because they had been dispersed far and wide, but when it was received for tax payment they were to be melted down and struck at the new standard.

Here is a good flow chart showing the changes of the denarius over time;

http://www.forumancientcoins.com/numiswi...Type%20Set