The reason is that the vellum refers to a parchment made from calf skin. The skin is removed from the animal and its hair or flesh, too. It is with that skin that the parchment maker or parchminer creates the vellum.
It was used instead of paper to write important texts and it was considered a strong material.
Sparta wanted to overthrow the Athenian oligarchy. Athens wanted to become the most powerful city-state in Greece. Sparta and its allies felt threatened by Athens's growing power.
