The present invention provides a casing assembly for a gas turbine engine comprising a radially inner casing and a radially outer casing. The assembly further comprises an axial mounting arrangement for mounting the inner casing and outer casing in a fixed axial relationship. The axial mounting arrangement allows radial movement of the outer casing relative to the inner casing such that distortion of the inner casing as a result of engine carcass loads on the outer casing is obviated as the inner casing is radially isolated from the outer casing.