Ferz

The ferz was the counselor placed beside the king in shatranj and in medieval forms of chess. Its name comes from a Persian word associated with a counselor or vizier. It could move only one square diagonally.

This made it a very short-range piece. Because every diagonal step preserves the square color, a ferz starting on a light square could never reach a dark one, and the reverse was also true.

In Europe, the piece's identity and power changed gradually until it became the queen. When studying an old position, mentally replacing the ferz with a modern queen completely alters attacks, king safety, and the consequences of pawn promotion.