The Attic (or Herodianic) system of numerals was the first numeral system used in ancient Greece. "Attic" refers to the Greek territory of Attica, while "Herodianic" refers to Aelius Herodianus, a grammarian of the 2nd century A.D. who described the system in his writings.
This system, which arose around 500 B.C. or so, used only six symbols. The number 1 was represented by | (a vertical bar), but the other five symbols were Greek letters:
This system is is also referred to as the acrophonic system because these last five symbols represent the first letter of the Greek words for 5, 10, 100, 1000 and 10,000 respectively.
There were two ways of combining these six symbols into other numbers. The first was that a small numeral atop Γ represented a multiplier. For example, represented 5 × 100, or 500. The second way was to write symbols next to each other, like Roman numerals. For example, ΔΔΔΔΓ|| represented 10 + 10 + 10 + 10 + 5 + 1 + 1, or 47. The symbols were usually written in descending order, but not always. Of course, with a non-positional number system, the order that symbols are written in is usually not important.
There is no "standard" way of writing fractions with this numeral system, as this system was typically not used for representing fractions.
Attic numbers were replaced by the Ionic number system between 100 B.C. and 50 A.D.
More Greek mathematical history.
Sources used (see bibliography page for titles corresponding to numbers): 14.