the fortress of arad is a fortification system built in the city of arad, on the left bank of the mureş river in the 18th century at the direct order of the habsburg empress maria theresa. the fortress lies today in the subcetate neighbourhood of the city, on the former military border between the habsburg empire and the ottoman empire. the fortress has been used during its existence as a military garrison, a military prison and today it is the home of the mixed romanian-hungarian battalion since 1999.