The prodromoi (from ancient Greek pródromoi) are the scouts of the army of Alexander the Great in his expedition to Asia.
The sources (Enabasis of Arrian essentially) mention the existence of four squadrons of light cavalry acting as scouts and skirmishers:these are 900 cavalrymen who pass through Asia under the command of Cassandra at the start of the war ( Diodorus of Sicily XVII, 17, 4), and which could be of Thracian and Peonian origin. The identification between the troops mentioned by Arrian and Diodorus is not entirely certain, however.
The prodromoi wear a helmet (Phrygian then Boeotian) as the only defensive weapon, and are armed with the xyston under Philip II, then the sarissa under Alexander. They are no longer mentioned after 330 BC. AD, date from which they may be found under the two units of hippacontistai (mounted javelin throwers) and sarisophoroi hippeis (horsemen carrying sarissa), whose functions correspond well to those we previously attributed to the prodromoi.
Historiography (Bosworth 1980, Hammond 2001) tends to show that they are also Macedonians. They may correspond to units of first assignment of young Macedonians, before being later poured into the heavy cavalry of the hetairoi.