How was reconnaissance performed in medieval warfare?

Question

During the middle ages reconnaissance played at least a minor part in a tactician's plans. As evidenced by this question Irish Hobelars would be used to scout ahead in terrain that was too difficult for heavy cavalry to traverse. But apart from this type of light cavalry I have not heard of any implementation of scout troops beyond seeing that occasional reports were returned by scouting forces.

How was reconnaissance performed during medieval marches? Did scouts ride ahead far enough to set camp and wait for their army to catch up to them, or would they perform scouting missions and return to the main force in one full outing? Similarly, what were their main tasks? Identify the opposing force, identify advantageous terrain, or perform other operations?

For the purposes of the question I'm curious about how scouting was performed during the period of the Hundred Year's war as I am interested to determine if that predates modern scouting techniques or if the it has remained relatively consistent over time.

Answer 1

The answer for the specific period of the Hundred Years war is separated in the following parts:

• English operations: English armies performed two types of operations: raids, with a set of military elements that were tasked with loot and wait for any opponent forces to engage. And big fighting-ready armies, that were tasked with conquering a city and fight big battles such as Agincourt, Crecy....

For the first type of operations, recon was not performed, besides groups of horsemen that were looting there and there and sometimes found enemy groups. Overall, those operations, largely performed far from Paris, did not encounter resistance so recon was not a need. But as time went on, this proved bad: an English raiding group was destroyed by Bertrand DU Guesclin's army West of Paris.

For English royal army, recon was not performed on a theoretical scale: no units were set to perform long range recon, however there were of course units guarding flanks to avoid surprise. But if you look at battles as Agincourt for example, there is a scenario where French Army surprise the English army on a strategic scale, but is too slow to attack immediately and let the time for English soldiers to entrench themselves and ultimately repel French assaults.

• French operations neither emphasized recon, because they had far more problems to overcome before this. But at time went on, French chiefs used the number of cavalrymen to check out English positions and attack accordingly. This is for example what allowed the French to attack English convoys during the Battle of Herrings... but this battle is ultimately a French defeat.

Conclusion:

No specific units existed to perform recon by that time, as the main cavalry was heavy knight cavalry and only poor or apprentice knights were light enough to perform recon. Recon largely used the civilian population to gather intelligence. There were no doctrine to perform "battle recon" with mobile and fighting units, although some light cavalry fights might have occurred marginally.

Answer 2

I'm not sure this fits the criteria of your question, but the De Velitatione Bellica gives a lot of information pertaining to reconnaissance by the Byzantine army in the context of the Arab-Byzantine wars (10th century, written for the emperor Nikephoras Phokas). You can find it in "Three Byzantine military treatises" by George Dennis.