A very rare type of denarius of Casimir the Great.
Issued by the mint in Kalisz, with a characteristic iconography: a crowned bull's head on the reverse. Its municipal origin is evidenced by its legend: MONETA KALIS.
In Edmund Kopicki's Index, it is described as R8, with a note about 3 known pieces.
Obverse: piast eagle. In the rim: [+ K REGIS] POLONI.
Reverse: crowned bull's head in front. In the rim: [+ COIN] KALIS