The Servian Wall is the earliest known defensive wall built around the city of Rome. Dating back to the 3rd century BC, it stands as an important example of ancient Roman engineering. Its main purpose was to protect the growing city from possible invasions and attacks.
This wall offers a close look at the methods used by Roman builders over two thousand years ago. Large blocks of tufa, a type of volcanic rock found in the region, were used to construct the wall. The choice of tufa made the structure both sturdy and practical for the tools available at the time. Well-preserved sections of the Servian Wall still exist today, allowing visitors and historians to study the techniques and materials that shaped early Roman architecture.
Source - https://en.wikipedia.org/wiki/Servian_Wall