On August 14, 1435, a formal contract of "brotherhood and friendship" between Serbia and the Republic of Venice was signed in Smederevo's audience hall. This contract resulted in Đurađ and his sons being counted as Venetian citizens. In early June 1439, the peace with the Ottomans, which had been gained through Mara's marriage to the Sultan, was broken. Led by Murad II, 130,000 Turkish soldiers occupied the hills around Smederevo. Branković rushed to Hungary for help, leaving his son Grgur in command. Help was not forthcoming, but Smederevo withstood the attack, even when Murad brought in cannons.