The territory of a duke or duchess is called a castle fief manor duchythe territory of a duke or duchess is called a duchy.

The territory of a duke or duchess is called a Duchy.

duchy

Explanation:

The term duchy is the medieval country territory that was ruled by the dutch and the duchess are a  high ranking nobleman second to the king or queen and term is almost exclusive to Europe. At present, the territorial duchies that have become very rare and the most dukedoms of the last few centuries have been of the purely ceremonial. Are all independent duchies have now disappeared.  In France, a number of duchies existed in the medieval periods in the places of Normandy, the Burgundy, the Brittany, and the Aquitaine.

It is c. naturally in the environment