the ancient mesopotamians seem to have utilized a cyclic theory of music, as seen through the numbering of their strings from the number one, through to the number five, then back down to one. through this, the pattern seems to arise that each string was used in separate parts of the music, the first string for the first part, the second string for the second part, and so on and so fourth. what makes the music cyclical is that the final string is tuned the same way as the first string, the second to last is the same as the second string, so the music will approach the fifth string then revert through the previous strings.