The invention relates to a maritime structure for laying the foundations of buildings, installations or wind turbines by means of gravity in a marine environment, which has significant advantages for constructing, transporting, positioning and operating same, owing to the novel features introduced into the design thereof in comparison with existing types. The structure comprises a base in the shape of a chamfered equilateral triangle, having a sufficient height to optimise navigability, the base being formed by a frame of vertical walls that form hexagonal or triangular cells closed at the ends by a lower slab and an upper slab, and three closed towers having a regular hexagonal or circular cross section which are located in the corners of the base. The structure can be towed, completely installed, with a wind turbine or superstructure that same supports, and has low initial draft, high naval stability and low resistance to movement. The anchoring process is performed by using gravity to ballast the cells with seawater, without needing any additional means, auxiliary large-capacity vessels or floating elements external to the structure itself. The structure can be positioned as a gravity foundation at a depth of 20 to 50 meters and can be re-floated to be transferred whole again to a port for dismantling.