The retaining wall can be made of different materials depending on what you prefer. A professional designer will be more than happy to go through these options and highlight what you can go with for your property.
In general, the options include brick, stone, concrete, and wood.
It's best to understand the pros and cons of each material before moving forward with a specific material. Greenville Landscaping will take the time to help out in this regard and personalize the design.