In Laredo, Building Development Services handles building permits, and a city ordinance says any wall taller than four feet "will require a building permit." For your own wall, especially one near that height, call them at 956-794-1625 to confirm what applies. When a permit is needed, we pull it as your hired contractor, so you don't take on the contractor's role yourself.
Some lots need more than a permit. Inside a 100-year floodplain, the city says retaining walls are built of reinforced concrete or other materials approved for the site, and special structural designs go to the City Engineer with calculations for approval. Where the city calls for an engineer's certification, that engineer has to be licensed to practice in Texas.
The ground here is the other reason every wall gets its own design. Much of Webb County is clay that's sticky when wet and rock-hard when dry, and large parts of it swell and shrink with moisture. Some areas flood now and then, and in places bedrock sits within 40 inches of the surface. We run into all of that on jobs across Laredo and the cities around it.