Select from the English alphabet only those letters, and just once each, which represent Roman numerals. Place them in a special order to represent a year in history that holds significance.
What is that year, and what are at least two reasons for that significance?
It is a special order in that the roman numerals are in their natural order (biggest first), which of course leads to the biggest value, because they are all additive in this order.
And "Annus Mirablis" is latin, which fits well with the title of the problem.
Assuming this is correct, all credit goes to Daniel and Charlie.
My two cents (spoiler)
