Once you’ve dug your trench and laid your paver base, you’ll need to use a level to ensure the gravel is flat before you start laying your retaining wall blocks. This is the most challenging part of the process, but it’s critical to make certain that the first layer is completely level. If not, the courses on top will gradually get more and more uneven. In that case, you’ll need to remove the pavers and start over from the bottom.