Abstract: A rotary rockwheel assembly (1) is provided for cutting a narrow trench in the ground when driven along the ground by a vehicle. The assembly (1) comprising a support frame (14), ground-engaging skids (17) on the support frame (14) permitting the support frame to be moved in the direction in which the trench is to be cut, and a rotary cutting wheel (2) carried by the support frame (14). A hydraulic drive motor (8) rotates the cutting wheel (2) about a substantially horizontal axis, and pivot rams (18) serve to lower the cutting wheel (2) relative to the support frame (14) from a raised position in which substantially the whole of the cutting wheel (2) is above the surface (5) of the ground to a lowered position in which a substantial part of the cutting wheel (2) is sunk into the ground in a trench (33) cut by the cutting wheel (2). Such an assembly is capable of cutting a trench in a particularly efficient manner.