1. The problem asks about the maximum safe height of different types of retaining walls. 2. Retaining walls are structures designed to hold back soil or rock from a building, structure, or area. 3. The maximum safe height depends on the type of retaining wall, soil conditions, and design factors. 4. Common types include gravity walls, cantilever walls, anchored walls, and sheet pile walls. 5. Gravity walls typically have a maximum safe height of about $3$ to $4$ meters. 6. Cantilever walls can safely reach heights of about $6$ to $7$ meters. 7. Anchored walls and sheet pile walls can be designed for heights greater than $7$ meters, depending on anchoring and soil conditions. 8. Therefore, the maximum safe height varies but generally ranges from $3$ meters for simple gravity walls up to $7$ meters or more for advanced types. 9. Always consult engineering standards and soil analysis for precise design limits.