One of the reasons behind the lack of inland open spaces in the plan was the belief of the Commissioners that the public would always have access to the "large arms of the sea which embrace Manhattan Island", the Hudson and East Rivers, as well as New York Harbor. They considered that if New York was a city such as Paris or London, located along the relatively small Seine and Thames River, then more parkland "for the benefit of fresh air and consequent preservation of health" would have been necessary. The Commissioners did not consider the proliferation of roadways, docks, wharves, rail yards, quarries and commercial sites which would essentially block the public from access to the rivers until the late 20th century, when a combination of factors began to make the riversides once again accessible, at least in narrow strips of greenways.