Kingdom started to prosper again, having fallen into a parlous state following the Mongol invasion. Charles exalted the cult to Saint Ladislaus I, using him as a symbol of bravery, justice and purity. He also venerated his uncle, Saint Louis of Toulouse. On the other hand, he gave importance to the cults of the princesses Saint Elizabeth and Saint Margaret, which added relevance to the lineage inheritance through the feminine branches. Charles restored the royal power which had fallen into feudal lords' hands, and then made the lords swear loyalty to him. For this, he founded in 1326 the Order of Saint George, which was the first secular chivalric order in the world, and included the most important noblemen of the Kingdom. Charles married four times. His fourth wife was Elizabeth, the daughter of Władysław I of Poland. When Charles died in 1342, his eldest son by Elizabeth succeeded him as Louis I. In the first years of his reign, Louis was advised closely by his mother, making her one of the most influential personalities in the Kingdom. Charles had arranged the marriage of his second son, Andrew, with his cousin Joanna, the granddaughter of King Robert of Naples, in 1332. Robert died in 1343, bequeathing his kingdom to Joanna but excluding the claim of Andrew. In 1345, a group of noble Neapolitan conspirators murdered Andrew at Aversa. Almost immediately, Louis declared war on Naples, conducting a first campaign in 1347–1348 and a second in 1350. He eventually signed peace with Joanna in 1352. Louis also waged wars against the Serbian Empire and the Golden Horde, restoring the Hungarian monarchs' authority over territories along the frontiers which had been lost during the previous decades. In 1370 Louis's uncle, Casimir III of Poland, died without male issue. Louis succeeded him, thus establishing the first union of Hungary and Poland. This lasted until 1382 when Louis himself died without male issue; his two daughters, Mary and Jadwiga, then ascended the thrones of Hungary and Poland respectively. The Age of Sigismund Louis I of Hungary always kept good and close relationships with the Holy Roman Emperor Charles IV of Luxembourg and finally proclaimed Charles's son Sigismund of Luxembourg to succeed him as King of Hungary. Sigismund became a renowned king who created many improvements in the Hungarian law system and who rebuilt the palaces of Buda and Visegrád. He brought materials from Austria