Dropped by Lothric Knights who wield them.
The Lothric Knight Greatshield is the first available greatshield, a massive tower shield with 100 Physical damage resistance. It has fair resistance against Magic damage, but falls short in terms of Lightning defense.
While effective against physical damage, this shield can also be particularly useful against enemies that deal Magic damage such as the Crystal Sage and the Sage's Devouts located in the Road of Sacrifices. One may also get use of it when going through the Grand Archives, another location where Magic damage is prevalent.
Reinforced with Titanite.