Great Portland Street is a street in the West End of London, which forms the boundary between Fitzrovia to the east and Marylebone to the west. Like the better known Portland Place which runs parallel with it to the west, Great Porland Street was developed by the Dukes of Portland, who owned most of the eastern half of Marylebone in the 18th and 19th centuries. It is now a mixed use street with buildings of mainly five to eight storeys. There are some offices and a number of blocks of mansion flats.