There was once a Duke who had an awkwardly shaped duchy, laid out like this:

       XX
 XX  XXXX
 XXXXXXX
XXXXXXXXX
XXXXXXXXX
 XX  XXXXX
 XX XXXXXX
    XXXXXX
     XXXX
     XX

Each X represents a 1000-hectare square.

The Duke was out of favor with the King, and when it came time for the Duke to pass down his land, the King hatched a plan to break up the Duke’s holdings (and thus the political power of his heirs). The King proclaimed that the Duke must split all of the land among his heirs such that:

1) The land is split into at least two pieces, and
2) Every piece has the same shape and size, allowing for rotations and/or reflections of the shape.

What are the largest pieces the Duke can break his duchy into, in accordance with the King’s edict?