By: Jacqui Palumbo
(CNN) — Half a millennium ago, the Protestant rebel priest Martin Luther sent out a number of small paintings as a marital announcement with political implications. He'd commissioned German painter Lucas Cranach the Elder to commemorate his controversial union with the nun Katharina von Bora in 1525 through complementary round portraits concealed in wooden boxes. Before long, their allies had received the secretive gift that boldly rejected Catholicism's rules around clerical celibacy.