John's marriage to the Hungarian princess Piroska involved him in the dynastic struggles of the Kingdom of Hungary. In giving asylum to Álmos, a blinded claimant to the Hungarian throne, John aroused the suspicion of the Hungarians. The Hungarians, led by Stephen II, then invaded Byzantium's Balkan provinces in 1127, with hostilities lasting until 1129. The Hungarians attacked Belgrade, Nish and Sofia; John, who was near Philippopolis in Thrace, counterattacked, supported by a naval flotilla operating on the Danube. After a challenging campaign, the details of which are obscure, the emperor managed to defeat the Hungarians and their Serbian allies at the fortress of Haram or Chramon, which is the modern Nova Palanka. Following this the Hungarians renewed hostilities by attacking Braničevo, which was immediately rebuilt by John. Further Byzantine military successes, Choniates mentions several engagements, resulted in a restoration of peace. The Danube frontier had been definitively secured.