POSTMA, F. J. Sevenster, De stenen man. Caspar de Robles, stadhouder van Friesland, Groningen en Ommelanden van 1572-1579. BMGN - Low Countries Historical Review, [S. l.], v. 102, n. 2, p. 287–288, 1987. DOI: 10.18352/bmgn-lchr.2827. Disponível em: https://bmgn-lchr.nl/article/view/URN%3ANBN%3ANL%3AUI%3A10-1-103174. Acesso em: 7 feb. 2023.