Aristarchus of Samothrace (c. 217 - 145 B.C.), a grammarian, headed the Library of Alexandria in the mid-second century B.C. after Aristophanes of Byzantium. In the ancient world Aristarchus was known for establishing the authoritative edition (diorthosis) of the main works attributed to Homer, the Iliad and the Odyssey.
Aristarchus used 6 critical signs for marking the Homeric texts, according to Reynolds and Wilson's Scribes and Scholars:
- obelos (devised earlier |) - a horizontal mark in the margin marking something spurious
- diple (>)marking something noteworthy in language or content
- dotted diple (> with dots above and beneath) to mark a verse that differed in Aristarchus' text from the text of Zenodotus
- the asteriskos (whence, asterisk) to mark a verse incorrectly repeated elsewhere
- asteriskos + obelos to mark interpolation of verse from elsewhere
- antisigma (a sideways u-loop) to mark a passage where the lines were reversed.