"pre-cursors," "runners-before," or "runners-ahead") implies that these cavalry 'moved before the rest of the army' and were therefore intended for scouting and screening missions.
Their members were, therefore, considerably poorer than the citizens who made up the Hippeis, the heavy cavalry, who were drawn from the second census class.
Circumstantial evidence suggests that this unit was 200-strong (the hippotoxotai are recorded as being 200-strong, the prodomoi, being their immediate successors, are assumed to have had the same strength).
[3] In the Macedonian army of Philip II and Alexander the Great, the cavalry unit termed the prodromoi carried skirmishing equipment for scouting and outpost duties, however, the cavalrymen of this unit are sometimes referred to as sarissophoroi, "pikemen" or "lancers", which leads to the conclusion that they were sometimes armed with an uncommonly long xyston (believed to be 14 ft long), though certainly not an infantry pike (sarissa).
[4] At Gaugamela, the prodromoi under Aretes were responsible for finally routing the Persian left wing cavalry, winning the battle in this sector.