AE3

Copper coinage of the Roman empire falls into two major groupings. Let's call the first the "old" age and the second the "new". In the old age, roughly up to the year 200 A.D. or so, copper coins were rather large because their face value matched the raw bullion value of the coin itself. As copper became scarce, and thus more valuable, this scheme became impractical. While the old denominations of Sestertius, Dupondius and As survived well into the 3rd century, the coins themselves became less common as the various rulers steered the public into using token coinage. That is, coins whose values were tariffed significantly higher than the worth of the metal it was made from.
The new age is born from this shift in the money supply. The public begrudgingly had no choice but to use the low-value coins being pumped out of the mints. However, because these same coins could not be redeemed in precious metal for what face value stated, inflation became rampant. As the mints helplessly tried to cope by working overtime, even the traditional silver washes became too expensive and were dropped entirely. Eventually copper itself became a scarce commodity and, as a last resort, the size of the bronze coins diminished from the familiar AE2's to AE3's and finally to AE4's as little as pencil erasers.
With this information, we can usually tell what period a coin belongs to even when its details have been obliterated.