What empire conquered almost all of Europe?

The Roman Empire conquered almost all of Europe, reaching its height in the 2nd century AD. It extended its territory across the Mediterranean and into regions that are now part of modern-day countries like Italy, France, Spain, and parts of Britain. The empire's vast network of roads and cities facilitated administration and trade, contributing to its influence and power across the continent. However, its dominance eventually declined, leading to its fragmentation and the rise of various successor states.