Cistercian monks invented a numbering system in the 13th century.  These are numbers 0-9.  I assume 0 as a single line.  The way the system worked for 1-9 these positions represent the first digit of a number.  The tens digit uses the same pattern but on the left side of the bar.  Hundreds moves to the bottom on the right and thousands are on the bottom left.  Any number between 1-9999 can be represented with this one symbol.