Take some railroad ties, rebar and gravel, and you have all the materials for building a simple retaining tie wall, like the guys at Such and Such Farms did.
Fortunately for everyone, they also documented all the major steps on how to build a retaining wall with railroad ties, complete with some great pictures.
The entire project is relatively simple and requires few specialized tools outside of an auger bit, a big drill and a few heavy hammers.
More details for crosstie retaining walls at: Building a Retaining Wall With Railroad Ties