Frombork (ˈfrɔmbɔrk; Frauenburg ˈfʁaʊənbʊʁk) is a town in northern Poland, situated on the Vistula Lagoon in Braniewo County, within Warmian-Masurian Voivodeship. As of December 2021, it has a population of 2,260. The town was first mentioned in a 13th-century document. In the early 16th century it was the residence of the astronomer Nicolaus Copernicus, who used it as a site for several of his observations. The town and its 14th century cathedral were badly damaged in World War II. After the war the cathedral was meticulously reconstructed and is again a popular tourist destination, listed as a Historic Monument of Poland. Frombork is known as “The Jewel of Warmia” because of its many historical sites. The Museum of Copernicus in Frombork holds exhibitions related to the astronomer, as well as to astronomy in general, and includes a planetarium. One of the biggest attractions is also the annual International Festival of Organ Music, held every summer. The town was founded as a defensive stronghold on an Old Prussian site. In 1224 at Catania, Emperor Frederick II declared Prussia directly subordinate to the church and Holy Roman Empire. Later in the same year the pope assigned Bishop William of Modena as the papal legate to Prussia. With the imperial Golden Bull of Rimini, the Teutonic Knights were granted control of the region, which they subsequently conquered. According to a local legend, the Old Prussian inhabitants were baptised by Anselm of Meissen, a priest of the Teutonic Knights and the first Bishop of the Bishopric of Warmia which was created in 1242 by William of Modena. Supposedly when the stronghold's lord died, his widow Gertruda offered the settlement to the bishop, and in her honor it was named "Frauenburg" (German for "Our Lady's fortress", "Castrum Dominae Nostrae" in Latin). This name is not unique in German, as it usually originates in the construction of a fortified chapel, church, or monastery dedicated to the Virgin Mary or inhabited by nuns.