Answer: The coins were made from cheaper materials
Explanation:
The so-called Antoninian was introduced to the imperial monetary system around the year 215. Silver was equivalent to less than 50% of the material from which these pieces were made. Although, in theory, they corresponded to 2 denarii, they contained the weight of only 1 and a half denarii. The new currency was abandoned shortly thereafter, but reintroduced from 238 at the same time as the denarius production has now been set aside. At the time of Decius (249-251), the average weight of the Antoninian was 4 grams;
Throughout the 250s and 260s, however, the currency would experience such devaluation in its weight and the amount of silver that it possessed that could hardly be compared with the pieces made in the previous decades, causing a decrease in the use of coined money.
