They were young men, but hard and sinewy, with a bearing that comes only to men rendered desperate by adversity. They were clad in mail shirts and worn leather; swords hung at their girdles.> - A Witch Shall be Born
The stench of the tannery is easily identifiable in the major cities of the world and tanners are often relegated to the outskirts of cities or villages, preferably downstream.
Bark is the most common form of tannin used to convert hide into leather. During the process it breaks down into Tar, which is a useful catalyst for alchemists.