For hundreds of years Rome kept a close eye on the output of its coins. As there were only a few mints operational at any one time, with Rome itself reserving the lion 's share of this output, quality control and accurate bookkeeping was a task that the mint officials could handle without resorting to the practice of placing marks on the coins themselves to know what was going on. However, near the latter half of the third century, the quality of the coins had suffered greatly under the stress of inflation and a centralized system made for an impractical way of distributing the (cheaper) currency being made. It was at this time that mintmarking really began to take hold and, within a few years, the process had become the most intricate and methodical the world would ever witness.
 
Although silver and gold  would eventually get some mint marks here and there it was the low value bronze denominations which received full attention in this area. Oddly, down to the very last days before the fall of Rome even the sorriest little copper would be duly impressed with the mark of its city of origin and, frequently, its officina as well.
 
The big idea therefore was for the government to keep track of who was making what and how much of it. Specie in gold and silver had such tight controls that general accounting practices were generally sufficient to minimize corruption and fraud. Copper coinage on the other hand was being produced on a very massive scale. Each mint each year may have made hundreds of millions of coins and, not surprisingly, most were of the copper variety meant for general circulation. This scale of manufacture would not be repeated again until the industrial age so a system for all those coins coming into circulation was imperative.
 
The treasury 's primary need in accounting was to make sure the correct number of coins were being made to pay off the government 's expenditures. Each mint was therefore bound to a number of rules that they were to follow both for accounting as well as to ensure a supply of coins that were as seamless in terms of look and feel from one mint to the next. Designs were therefore carefully coordinated between the various mints and for specific lengths of time. The painstaking practice of ensuring that every single coin looked essentially identical from one end of the empire to the other and a level of detail that dictated the precise, hyper-correct placement of individual letters and other design elements can be considered as part of the quintessentially Roman way of precision engineering.
 
The very first mintmarks employed under the Roman imperial period usually consisted of cryptic symbols just meant to reveal the city of origin. This practice was far from widespread and given the normal variances from region to region it is now known without doubt that some coins were made in certain locations or at least general areas even without these mintmarks based on stylistic differences alone. But these differences were much too subtle for administrators to bother with. When the need presented itself the mint marking system was put into place and within a matter of a few years the practice was more or less standardized across hundreds of thousands of square miles.
No sooner than explicit mint marks begin appearing that identify each city of origin than it becomes necessary to break it down further into individual series and, as noted above, often the officinae involved too. A typical late Roman bronze will often carry additional symbols that reveal separate production runs.

 
Understanding this system is complex and their meanings are not always universally agreed upon. But generally speaking some conventions can be followed with enough consistency that they soon become familiar to the collector.
 
The first step then is to identify the name and location of all these mints. The  map on the following page identifies the main ones in operation during the fourth and fifth centuries.