Between 83 and 85, the
Romans constructed the Obernburg
castrum, named
Nemaninga, to guard the
Limes Germanicus which followed the Main river here. It was originally built from wood but in the middle of the 2nd century AD replaced by a stone fort. The castrum was the garrison of the
Cohors IIII Aquitanorum equitata. The stone fort, with an area of 2.9 ha and a nearly rectangular ground plan of roughly 185/188 × 160 m was oriented to the river Main. Obernburg's old town still somewhat corresponds to the castrum's footprint, with some of the thoroughfares corresponding to Roman streets, such as today's Römerstrasse which follows the course of the fort's
via principalis. On 25 March 1313, Obernburg was raised to town by
Archbishop of Mainz Peter of Aspelt. The confirmation of town rights by
Louis the Bavarian came on 27 July 1317 in a document issued in
Aschaffenburg. Until the
Reichsdeputationshauptschluss in 1803, Obernburg belonged to
Electoral Mainz. Thereafter it belonged to the newly formed
Principality of Aschaffenburg, with which it passed in 1814 (by this time it had become a department of the
Grand Duchy of Frankfurt) to the
Kingdom of Bavaria. The town became the seat of an
Amtsgericht. In 1872, the railway line Aschaffenburg to Miltenberg was opened, with a stop at Obernburg. The first local bridge across the Main was built in 1892. In 1915-7 the Main was channeled and the weir with lock and a hydroelectric plant was constructed. Until 1 July 1972, Obernburg was the seat of a like-named district. This was abolished in the course of municipal reform. On 1 May 1978, the neighbouring municipality of Eisenbach was amalgamated with Obernburg. ==Governance==