As part of the
Treaty of Venlo,
William of Jülich-Cleves-Berg was proposed a marriage to one of Emperor
Charles V's nieces, with William being allowed to pick between Maria and her sister,
Anna. The mental illness of her son Johann Wilhelm, born in 1562, was possibly inherited from his mother. The theory that the princess was sickly and therefore not a part of court life as well as the fact that she gave birth to six children in eight years might have taxed her already frail health and psyche and pushed her into mental confusion. Her paternal grandmother was
Joanna of Castile and much like her grandmother, she was regarded as moody and was at first temporarily and later entirely insane. == Death ==