 Upon Gian Gastone 's death on 9 July 1737 , Francis Stephen ceded Lorraine and became Grand Duke of Tuscany . In 1738 , Charles VI sent the young couple to make their formal entry into Tuscany . A triumphal arch was erected at the Porta Galla in celebration , where it remains today . Their stay in Florence was brief . Charles VI soon recalled them , as he feared he might die while his heiress was miles away in Tuscany . In the summer of 1738 , Austria suffered defeats during the ongoing Russo @-@ Turkish War . The Turks reversed Austrian gains in Serbia , Wallachia and Bosnia . The Viennese rioted at the cost of the war . Francis Stephen was popularly despised , as he was thought to be a cowardly French spy . The war was concluded the next year with the Treaty of Belgrade . 
