A gas turbine engine casing comprising: an inner circumferential wall; an outer circumferential wall spaced radially outwardly from the inner wall; wherein the inner and outer circumferential walls are formed by an axially repeating profile comprising an inner wall portion and an outer wall portion connected to one another by an intermediate portion, the axially repeating profile being arranged such that the inner wall portion abuts against and is connected to an adjacent inner wall portion to form the inner circumferential wall and the outer wall portion abuts against and is connected to an adjacent outer wall portion to form the outer circumferential wall.