Letters on Byzantine Coins

[Arnulf]

Hi...what do the large letters on the back of some Byzantine bronzes mean?  Particularly, I have an Anastasius I with a big "K" on the back and a Justinian I with a big "M"?

Thanks!

ADMIN NOTE: See Byzantine Denominations in NumisWiki.

[Steve Minnoch]

It is the denomination in a number of nummi. The letters are the Greek numerals (or sometimes Roman).

A follis (M) = 40 nummi
Half follis (K, or sometimes XX) = 20
Decanummuim (I) = 10
Pentanummium (E) = 5
Nummus (A) = 1

There are some others floating around such as 16 nummi pieces with IS.

Steve