Most historical buildings are concentrated in the Old Town. Bratislava's Town Hall is a complex of three buildings erected in the 14th–15th centuries and now hosts the Bratislava City Museum. Michael's Gate is the only gate that has been preserved from the medieval fortifications, and it ranks among the oldest of the town's buildings; the narrowest house in Europe is nearby. The University Library building, erected in 1756, was used by the Diet of the Kingdom of Hungary from 1802 to 1848. Much of the significant legislation of the Hungarian Reform Era (such as the abolition of serfdom and the foundation of the Hungarian Academy of Sciences) was enacted there.