Assembly of a tractor (T) with a three-point suspension (44-46) and a device (1) for performing activities on an agricultural land, comprising at least one tool beam (3,2,13), a portion of which on one side projects laterally with respect to the tractor and which comprises a number of juxtaposed tools (15), such as crop mowers, which are supported by the tool beam, wherein the tool beam is mounted to a support frame (20,6) which, at the location of a first (21), a second (22) and a third (23) mounting position, is mounted to the three-point suspension of the tractor, wherein the first mounting position and the second mounting position, respectively, are located at the end of the support frame which faces away from the projecting portion of the tool beam, and at a location between the first mounting position and the projecting portion of the tool beam, respectively, and the third mounting position is located above the first and the second mounting position, wherein the support frame is divided into a first support frame portion (6) on which the tool beam is mounted and a second support frame portion (20), wherein the first support frame portion (6) extends between the first mounting position (21) and the tool beam (3,2,13) and is rotatable in or near the first mounting position, in a hinge (30), taking along the tool beam, between an operative position and one or more break-away positions about an axis which has a vertical directional component and about an axis which has a horizontal directional component parallel to the direction of travel of the tractor, wherein the second support frame portion (20) defines at least the second and third mounting positions, wherein the first support frame portion is connected by means of a support device to the second support frame portion, which support device, at one or more locations which, viewed in a direction transverse to the direction of travel, are spaced apart from the first mounting position, movably interconnects the fi
