To build a timber supporting wall, start by digging a trench along the line of where your wall will be. The ditch should be roughly the depth and width of the timbers you'll be using to build the wall. If you want space to work on the back side of wall, dig that space out before beginning building the wall. Utilize a line level to level the ground where the timbers will lay.
Place the 1st row of timbers flat in the ditch.

After your first row of timbers is laid along ditch begin stacking your 2nd row of timbers.
Stagger the ends of the timbers to ensure a powerful wall. Attach each layer of timbers to layer below it with spikes ( eight in. long 60D nails ). Timber supporting walls are built straight up - not slanted like stone walls - so keep a level or plumb convenient as you stack them. Timber Tie-Backs If your wall will be higher than about 18 inches use tie-back timbers each 8 or 10 feet on numerous levels to hold your wall upright and ensure it won't fall forward thanks to the consistent pressure exerted on it from behind ( top failure ). To add a tie-back timber, simply lay one timber vertical to the other timbers but with its length extending into the area that'll be back filled.

When the area is back filled this timber will act as anchor to hold the wall in place and guarantee your timber main wall will last. Timbers United into One Structure One facet of my supporting wall design which is a little different from others you'll see is that I like to unite the whole timber main wall structure with re-bar driven vertically thru all of the timbers and into the ground through a hole that's drilled thru all of the supporting wall timbers after they're absolutely stacked. The re-bar should fit firmly into the drilled hole. This step could be an excessive but I like robust stuff that lasts a considerable time.

An alternative but similar strategy is to drive re-bar thru the bottom 2 or 3 layers when the wall is about half-built and then connect the bottom timbers to the top layers once the top layers are added ( see footage ). Use Correctly Treated Quality Timbers Some books and sites will counsel that you use "garden timbers " (those inexpensive ones with 2 round sides and 2 flat edges) to build a main wall but I strongly counsel against that practice because "garden timbers " are sometimes made of the least expensive pieces of wood leftover from the production of other lumber or plywood and contain often heartwood which doesn't accept pressure treatments. They'll possibly be heavily rotted inside a few years and will swiftly fail. Building a timber supporting wall is difficult work so use timbers which will last. You may even think about employing timbers with a vinyl or polymer coating. American Pole and Timber is a credible company that ships quality timbers countrywide and offers one or two types of vinyl coatings that will make wood last nearly for ever and ever.