This is the last group in Series Y, and the last of the Coriosolite coins. The tribe became absorbed, along with others into the expanding Roman Empire, and a culture embarked upon its death throes.
Group M was my Rosetta stone! The first coins that I tried to sort out were those of Classes I and III. Without realizing it at the time, I had endeavoured to start with the most difficult. I tried rearranging the designs a number of ways for months, all to no avail. At that time I was working under the assumption that the die engravers would cluster all like designs together. So - like many had probably done before, I grouped similar banners together. No matter how I did this, it never worked, and similar varieties of obverses could be found in each 'group' I tried to form. I was able to divide Class I and III, but Class III itself seemed impossible.
Finally, I noticed that on some coins the lash went from the banner to the pony's mane ornament, while on others the lash went from the banner to the driver's forehead. I separated these two features and noticed that in each group the designs of the pony's ears were different. Then I noticed that there was an exception to this and realized, in a flash, what was happening. The die engraver was evolving the design as he worked, and there were overlapping changes that would define the chronology!
Suddenly I had the key, and I managed to rough out the chronology for the whole series in a few hours - working at a feverish pitch, I realized afterward that I had memorized so much of the design elements, that once I knew how how the engraver worked on a few details, I got more and more of a 'feel' for how he was thinking about the designs. It was an eerie experience.