Inscriptional Parthian is one of three related ancient scripts, along with Inscriptional Pahlavi and Psalter Pahlavi, used for writing a number of Iranian and Indo-European languages. All three scripts developed from the Imperial Aramaic script.
Inscriptional Parthian was an abjad with twenty-two consonant letters but no vowel marks. It was written from right to left, usually with spaces between words. Seven ligatures were commonly used. Because of the script's Aramaic heritage, some words were written in the Aramaic language, but read as the appropriate Iranian-language word (much like the ampersand symbol, which is actually a ligature of the Latin word 'et' but is pronounced in English texts as the English word 'and'). These words are called xenograms.
Script-specific numbers were used in Inscriptional Parthian to represent the numbers 1, 2, 3, 4, 10, 20, 100 and 1000. These could be combined (added) to write any number, for example 58 was written with five signs, for 20+20+10+4+4. Unlike many modern Semitic scripts, numbers were written from right to left, the same direction as the text.