A system for laying an underwater pipeline along a path on a bed of a body of water, the system comprising: - a construction site to form a string of an underwater pipeline by joining together a curved portion and straight pieces of pipe so that the string includes at least one curved portion shaped substantially like a portion of the bed of the water body including an abrupt change in slope; - at least two vessels to transfer, in the body of water, the string from the construction site to a laying site in the body of water and substantially on the vertical of a path along which to lay the string, wherein the two vessels comprise respective winches connected to the opposite ends of the string and respective traction elements configured to be connected to the opposite ends of the string; - a plurality of floating devices coupled to the string and so as to selectively support and sink the string in the body of water, and progressively lay the string along the path on the bed of the body of water, wherein each floating device is configured to vary its own buoyancy; - a stabilizer device comprising a stay wire that defines a chord of the curved portion and is connected to the string and is configured to prevent deformation of the curved portion of the string; - a further vessel comprising a further winch connected to the curved portion of the string and a traction element connectable to the curved portion of the string; and - characterized in that a ROV is connected to the further vessel and configured to control the laying operations of the string on the bed of the body of water, wherein the information transmitted by the ROV enables controlling the steps of laying the string and governing the position of the vessels, the further vessel, the winches, the further winch, and the operations of the floating devices. - a construction site to form a string of an underwater pipeline by joining together a curved portion and straight pieces of pipe so that the string includes at least one curved portion shaped substantially like a portion of the bed of the water body including an abrupt change in slope; - at least two vessels to transfer, in the body of water, the string from the construction site to a laying site in the body of water and substantially on the vertical of a path along which to lay the string, wherein the two vessels comprise respective winches connected to the opposite ends of the string and respective traction elements configured to be connected to the opposite ends of the string; - a plurality of floating devices coupled to the string and so as to selectively support and sink the string in the body of water, and progressively lay the string along the path on the bed of the body of water, wherein each floating device is configured to vary its own buoyancy; - a stabilizer device comprising a stay wire that defines a chord of the curved portion and is connected to the string and is configured to prevent deformation of the curved portion of the string; - a further vessel comprising a further winch connected to the curved portion of the string and a traction element connectable to the curved portion of the string; and - characterized in that a ROV is connected to the further vessel and configured to control the laying operations of the string on the bed of the body of water, wherein the information transmitted by the ROV enables controlling the steps of laying the string and governing the position of the vessels, the further vessel, the winches, the further winch, and the operations of the floating devices.