# What was the symbol used for 'one thousand' in Ancient Rome?

I saw an episode of QI (Quite Interesting, a British 'quiz' show that just sort of presents trivia). I don't know the episode or when it was produced (I've searched for it on youtube but haven't found it yet).

On this episode one of the questions was "What symbol did the Ancient Romans use for 'one thousand'?". The answer, which everyone and myself thought, was "obviously 'M'".

But the show is all about contrarian facts. They said no, the 'M' was introduced in the Middle Ages and that the 'Ancient' Romans used some symbol that looked like '(I)' (with example photos).

Yet, that seems strange... I don't think I've ever seen anything other than 'M' used for the Roman digit for a thousand.

What is the real story?

The shortest answer is, often they didn't use anything! Roman numerals weren't frequently used for numbers greater than a thousand; accountants doing math with big numbers would have alternate systems that made adding and subtracting easier, and year numbers past 1000 weren't a concern.

However, there were a few types of specialized notations for this. One of them is called the apostrophus system, where a straight line with curves on either side indicated larger numbers. ⅠↃ is 500, ⅭⅠↃ is 1,000, ⅠↃↃ is 5,000, ⅭⅭⅠↃↃ is 10,000, and so on. Here's an example of a year given in this notation, on a plaque on a church in the Netherlands.

Sometimes these were combined into single glyphs, and thus you get Ⅾ, ↀ, ↁ, ↂ, and so on. The first of these was eventually re-analyzed as the letter D, which is how that became the symbol for 500. The rest generally fell out of use, and ↀ was replaced by M, the first letter in mille ("thousand"). (Though it's possible that the infinity symbol ∞ was, much later, adapted from ↀ.)

Another system, which became more popular for recording distances in Imperial times, was to put a bar over a number to multiply it by 1,000. In this system, a thousand would simply be I̅. This came about somewhat later, but still definitely qualifies as "ancient Roman".

• Excellent answer... but "accountants doing math with big numbers would have alternate systems "? Alternate systems? You can't tantalize us with that and walk away. Any ideas? Commented Jun 28, 2023 at 20:44
• @Mitch Unfortunately I don't know the full details of that, though I'll look into it!
– Draconis
Commented Jun 28, 2023 at 20:49
• @Mitch: Could be a nice follow-up question!
– Cerberus
Commented Jun 28, 2023 at 20:49
• @vsz: The Roman army is a clear example where they use strict unit size (first hit on Google). By having such a clear unit system and scoping the general logistics to those unit sizes, it means that the numbers themselves are kept low. Half a million soldiers would've been expressed as 100 legions. It not quite the metric system but the factor sizes between units are 8, 10, 6, 10 respectively; which is pretty close and effectively means that you never have to count more than 10 of anything (as you'd then move up to the bigger unit) Commented Jun 29, 2023 at 6:28
• Or it says 1630. Commented Jun 30, 2023 at 0:15