There are many achievements that made the Roman Empire one of the most powerful civilizations of the past. They include but are not limited to:
-<em>Architecture</em>
-<em>Political organization</em>
-<em>Strong Military</em>
-<em>Vast Size</em>
-<em>Systemic development (ties politics and architecture)</em>
The Romans developed many inventions and ideas that are still in use today and are commonly studied. Historians admire their meticulous architecture and urban planning. They strive to figure out how they developed settlements and established a proper republican democracy across a very vast space.
But of all the achievements, I'd say that their <u>inventions</u> are the greatest as their ideas and technology is still put to use today. Although there are enhancements in today's versions, we would not be able to make them without the Romans.