Novi Sad is the second largest city of Serbia. It began as a stone age settlement in present-day Petrovaradin. The Celts founded the first fortress at this location. During Roman rule, a larger fortress was built in the 1st century AD. It was devastated by the Huns in the 5th century and rebuilt by the Byzantines. The city passed through many other hands until being conquered by the Kingdom of Hungary. The city was first mentioned under the name Peturwarad or Petrovaradin in documents from 1237. It passed through the Ottoman Empire in the 16th century and the Habsburg Monarchy in the 17th.