I saw a comment on another subreddit that said that medieval archers were a lot more effective soldiers when compared to Roman archers. I was curious what were the advancements in weaponry, armor, tactics etc. between these two types of archers?
One major difference between Roman and Medieval archers is where the respective armies got archers from. The Roman army, notably, did not deploy their own archers. Most archers were recruited as auxiliary units from neighbours or as mercenaries, with the bulk of the Republic-era army being heavy infantry. As the Romans encountered more opponents in the east, such as the Parthians - who handed the Romans the crushing defeat at Carrhae with their combination of horse archers and cataphracts - they began to adopt more of the weapons and tactics of their enemies. Indeed, this trait is a hallmark of the Roman army throughout its existence. The Roman Empire, and later the Eastern Roman Empire, made more use of archers and horse archers. Their equipment, deployment and training methods can be seen outline in the Strategikon of Maurice.
In Medieval Europe, while armies had their own trained archers, we actually see a bigger shift towards the crossbow as the preferred weapon in continental Europe over the bow. The notable exception to this is the English longbow. After the wars with the Welsh, the longbow was adopted as a standard military weapon and more effort was focused into building a reliable corps of archers. The Assize of Arms 1252 stipulated the mandatory ownership of bows and arrows for every able-bodied man and child, with subsequent laws and proclamations in the following century mandating the practice of archery on Sundays, banning football in favour of archery practice and so on. The purpose of this was to instill a culture of archery, with the benefit of having a high portion of the population able to be recruited and trained as archers for military campaigns, and England was one of the few nations to maintain standing armies including archers. The cost of maintaining such a force was disproportionately high - England had to import wood from Spain and Italy and require merchants to procure arrow shafts in order to meet the extremely high demand. While not in service, English archers would find employment elsewhere as mercenaries, with Arthur Conan Doyle's The White Company being based on such a force.
In terms of equipment, the Roman army would have adopted the composite bow from their Asiatic neighbours and shot in the Eastern method, notably using the thumb draw and mostly based on horse archery. Medieval European archers (generally more in Western Europe) would have used self-bows (made from a single piece of wood, with yew being the most desirable) as opposed to the composite materials of wood, horn and sinew used in Eastern bows. The overall effect in the context of battle is not dissimilar - composite bows were more efficient for their compact size, while the massive self-bows used by the English (frequently referred to as "war bows") had extremely high draw weights (100-160lbs). The high draw weights meant that archers could easily penetrate padded armour (such as gambeson) and mail with ease.
In regards to tactics, the Roman armies mostly used their archers as a screening and skirmishing force, typically using them to open a battle and then withdraw to allow the infantry to carry the fight. The Medieval archer (again, highlighting the English as the exemplar) was deploy in massed formations in the thousands. The English archers not only acted as skirmishers to open a battle, but also established positions on the wings of their infantry, using high ground where possible and defending their position with stakes. The sheer intensity and volume of shooting (described as an "arrow storm") severely disrupted opposing armies (as in Crécy), creating beaten zones and funneling their enemies towards men-at-arms (Agincourt), or just outright massacring static formations (Falkirk, Halidon Hill).
In short, the Medieval archer was closer to what one would call a professional soldier (strongly depending on which region you are referring to), and was used by the English as a core part of their army, in some cases outnumbering the men-at-arms (and also doubling as light infantry if needed). When the conditions were right, the English archer-heavy armies were terrifying on the battlefield with few counters, and in many battles they played a significant role. In contrast, the Roman armies paid little attention to the use of their own archers (in early periods) and only used them in supporting roles (in later periods).
It's worth noting that one technological change would ultimately nullify the effect of medieval archers: plate armour. With increasing availability and quality of armour, archery reached its peak and would decline from the 15th century onward. This recent test by Tod's Workshop on YouTube demonstrates how armour design had caught up to the battlefield threat of archery.
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