All the peerage ranks were originally due to some certain service or position they did that became hereditary titles, but were each of those ranks responsibilities and privledges? I know only that marquess was in charge of marches, aka border lords
Since different courts and different languages developed their own system of titles - you don’t get earls outside of Britain or Scandivia, landgrave and freiherr have a very specific Germanic context - it sort of depends on which one you’re looking at.
But there are some etymological roots that can tell us what the original responsibilities of these different titles were (said roles shifted hugely over time):
- Duke originates from the Latin dux, and was originally a Roman title indicating the highest-ranking military commander in a given province.
- Count comes from the Latin comitem, meaning companion or delegate of the emperor, and was originally a Roman title indicating a high-ranking courtier, and the title continued to have this association with courtly service, see also count palatine, which referred to someone who served in the royal palace. Viscount comes from the Latin vice-comitem, meaning the deputy of a count.
- Earl, which is pretty much only used in Britain and Scandinavia, comes from the Anglo-Saxon and means chieftain.
- Marquess/Marquis does indeed refer to a lord who holds land on the borders, and thereby has additional responsibilities of defense and fortifications and additional privileges to go along with that.
- The etymology of Baron is a bit contested, but is generally held to originally be a military title similar to dux, although indicating a lower rank.