The second half of the 14th century and the entire 15th are believed to have been a period of rapid development for Konin. During the reign of the Polish King Casimir III the Great (1310–1370), a king's castle was erected in Konin and the town was encircled with walls and a moat, marking the beginning of Konin as a king's town Later, King Władysław II Jagiełło (1351/52 - 1434) was a guest of Konin, visiting in the years of 1403, 1425, and 1433. (Władysław engineered a historic debilitation of the political and military power of the Teutonic Knights by means of his Polish-Lithuanian victory at the Battle of Grunwald in 1410.) His last stay at Konin, in 1433, was his longest. Throughout that year's summer, he resided in the town's castle, obtaining reports on a Polish retaliatory strike against the Knights.