Thereupon he erected a four-story gristmill extending out over the creek, whose power was supplied by the alternate ebb and flow of the tide against its undershot wheels.1 Alexander was succeeded in his property rights by his son Robert, who, not satisfied with the supply of water for the mill, procured a grant to build a dam across the Harlem River from Bussing's Point, oi) the Harlem side, to Devoe's Point, on the Westchester side, "so as to hold the waters of the river for the benefit of the mill at Kingsbridge, thus practically making a tidal millpond between the present site of the Central Bridge at Seventh Avenue and <dd King's Bridge. This erection was known for years as Macomb's Dam. But it was required in the act that Macomb should so construct the dam as to permit boats to pass, and thai he should always have a person in attendance to afford the desired passage. He neglected, however, to conform to this direction, and not only erected his dam without the specified contrivance, but converted the lip of GENERAL ALEXANDER MACOMB. the dam into a permanent bridge and collected tolls from everybody who crossed it. The utter obstruction to the navigation of the river thus introduced continued until 1838, when, as we shall see, it was forcibly removed by the enterprise and courage of a number of citizens of Westchester, and the mischievous and unwarranted interference with tin1 natural function of the Harlem River as a public waterway was brought to an end. Macomb's Dam was the only absolute barrier to the progress of vessels coming up the Harlem River. But it had a rival in Coles's Bridge, tin1 site of the present Third Avenue Bridge -- which indeed antedated it. In 1790 the legislature granted to Lewis Morris the right to construct a bridge from Harlem to Morrisania, which was 1 This