a marine structure comprising a plurality of hollow vertical columns tied permanently together by bracing elements at their lower and upper portions with cross bracing elements within their lengths to form a rigid tower , the columns having hollow feet open at their lower ends to be sunk into a sea bed , an excavating mechanism inside the feet for excavating sea bed material . each column of the structure is floatable in water and is provided with inlet through which ballast may be introduced to sink it vertically in the water . a method of constructing a marine structure comprising making a plurality of hollow columns , bracing the columns together at their end portions and between their end portions to form a horizontally disposed rigid buoyant structure such that when erected on the sea bed no horizontal bracing members are in the critical wave zone , assembling hollow feet on the columns , floating the structure to the site with the columns substantially horizontal , ballasting one end portion of the columns to upend the structure into a substantially vertical position and to sink the structure onto the sea bed , and excavating the sea bed within the feet to enable the structure to be seated firmly in the upright position at a suitable foundation depth in the sea bed .