This tiny and somewhat irregularly shaped brick church is all that remains of the Piast dynasty’s 13th-century Royal Castle, which once stood on the island. St. Martin’s too, however, was largely rebuilt in the 15th and 20th centuries. Before WWII the church was a centre of Polish culture in a primarily German city. Poles gathered here to hear sermons and sing hymns in their own language. The last Polish mass under Nazi oppression was held here in 1939. A plaque outside reads in part, “We are Poles... A Pole is a brother to a Pole... Poland is our mother, we cannot speak badly of our mother.” Outside St. Martin's stands a massive monument to Pope John XXIII, placed here in 1986.