Fortification innovations in the Grand Duchy of Lithuania during the reign of Sigismundus Augustus (1548-1572) - Baronas, Darius (Zamek i dwór w średniowieczu od 11 do 15 wieku : Materiały 19 Seminarium Mediewistycznego. [The castle and the court in the Middle Ages from the 11th until the 15th century. Materials of the 19th Seminar of Medievalists]., 2001)