I am announcing a web page on the coins of Diocletian:
http://augustuscoins.com/ed/tetrarc...anCoins.html br /
Diocletian, 284-305, had a large and lasting impact on the course of the Roman empire. His coins would make a worthy sub-collection. The page discusses the events that show in the coinage. For example,
Event 6) Trier (and only Trier) minted FORTVNA REDVCI types for the safe returns of emperors from their travels.

Diocletian
IMP DIOCLETIANVS PF AVG
FORTVNAE REDVCI AVGG NN
Fortuna seated left, holding rudder on globe and cornucopia
*
TR
RIC Trier 230a "c. 298-9."
Sear 12755. Failmezger 4.
According to RIC, the first issue (distinguished by this mintmark TR, as opposed to BTR or ATR) refers to
"Constantius' successful Rhenish campaigns" and possibly the conclusion of his British campaign in 296-297, and
"Heraclius' [Maximian's] African campaign (followed by his visit to Rome)" which followed his return from the Rhine (on his way to Africa).
Again, here is the link:
http://augustuscoins.com/ed/tetrarc...anCoins.html