fought in the Russo-Crimean Wars. Prompted by the Russian invasion, Livonia first unsuccessfully sought help from Emperor Ferdinand I, then turned to Poland–Lithuania. Landmeister von Fürstenburg fled to Poland–Lithuania to be replaced by Gotthard Kettler. In June 1559, the estates of Livonia came under Polish–Lithuanian protection through the first Treaty of Vilnius. The Polish sejm refused to agree to the treaty, believing it to be a matter affecting only the Grand Duchy of Lithuania. In January 1560, Sigismund sent ambassador Martin Volodkov to the court of Ivan in Moscow in an attempt to stop the Russian cavalry rampaging through rural Livonia. Russian successes followed similar patterns featuring a multitude of small campaigns, with sieges where musketmen played a key role in destroying wooden defences with effective artillery support. The Tsar's forces took important fortresses like Fellin (Viljandi), yet lacked the means to gain the major cities of Riga, Reval (Tallinn), or Pernau (Pärnu). The Livonian knights suffered a disastrous defeat by the Russians at the Battle of Ērģeme in August 1560. Some historians believe the Russian nobility were split over the timing of the invasion of Livonia. Eric XIV, the new King of Sweden, turned down Kettler's requests for assistance, along with a similar request from Poland. Kettler turned to Sigismund for help. The weakened Livonian Order was dissolved by the second Treaty of Vilnius in 1561. Its lands were secularised as the Duchy of Livonia and Duchy of Courland and Semigallia and assigned to the Grand Duchy of Lithuania. Kettler became the first Duke of Courland, in doing so converting to Lutheranism. Included in the treaty was the Privilegium Sigismundi Augusti by which Sigismund guaranteed the Livonian estates privileges including religious freedom with respect to the Augsburg Confession, the Indygenat, and continuation of the traditional German administration. The terms regarding religious freedom forbade any regulation of the Protestant order by religious or secular authorities. Some members of the Lithuanian nobility opposed the growing Polish–Lithuanian union and offered the Lithuanian crown to Ivan IV. The Tsar publicly advertised this option, either because he took the offer seriously, or because he needed time to strengthen his Livonian troops. Throughout 1561, a Russo-Lithuanian truce (with a scheduled expiration date of 1562) was respected by both sides. Danish and Swedish interventions In return for a loan and a guarantee of Danish protection, Bishop Johann von Münchhausen signed a treaty on 26 September 1559