Install the foundation and first three courses of the timber wall with timbers, landscaping screws and a drill. Back-fill any gaps in the foundation with gravel. Tamp the gravel down with a 4-by-4-inch board for drainage.
Build a deadman anchor to install every 4 feet down the length of the wall. Use a circular saw to cut two 3-foot lengths of 4-by-4-inch boards for each deadman anchor. Position the boards into a T shape and drive a 12-inch spike through the top of one board into the end of the other with a hammer.
Unroll a strip of landscape fabric and cut it with scissors to fit against the back of the wall. Mark the spot on the fabric where the deadmen anchors will hit and cut holes in the fabric in these spots.
Lay the fabric against the back of the wall and use a shovel to back-fill the first two courses with gravel and soil. The gravel should fill a 6-inch-wide section directly behind the wall, and the soil should be filled in behind the gravel.
Lay the deadmen anchors on top of the back-fill so the long end of each goes through the fabric and against the third course of wall timbers. Hammer 12-inch spikes through the front of the wall into the end of each so the top of the T shape runs parallel to the wall 3 feet away.
Stake the ends of the deadmen anchors with 12-inch spikes to secure them to the ground. Back-fill the space around them with gravel and soil and tamp it with the 4-by-4.
Continue to build up the walls with landscape timbers until you reach the intended height. Back-fill each course with gravel and soil as you go.