Emergency coin of three pennies of siege of Groningen; emergency coin minted to pay those who helped to fortify the fortifications; unilateral emergency coin. Obverse: double-headed eagle below letter G above coat of arms between years; under the left eagle's head a star; under the right head a ring. Reverse: blank; Groningen; anonymous; 1591; brass (alloy); striking (metalworking); d 2.2 cm x w 3.68 gr