An inertial sensor arrangement comprises a fiber gyro which responds to the horizontal component of the angular rate of the earth. A fiber coil of the fiber gyro is arranged at a positioning frame which is supported for rotation about a vertical axis relative to a housing. The positioning frame can be rotatably adjusted and mechanically locked into three fixed positions. Signals obtained thereby provide a measured value of the angle formed between a reference direction and north. Inclination sensors are provided for determining the inclination of the inertial sensor arrangement. The fiber coil inclusive of the positioning frame and two inclination sensors are mounted at a rigid sensor block which is connected to the housing in heat insulating manner.