Because they were tolerant of different beliefs and encouraged trade between different cultures along the Silk Road, ensuring the safety of traders traveling along the trade routes.
The most straightforward theory for Western Rome's collapse pins the fall on a string of military losses sustained against outside forces. Rome had tangled with Germanic tribes for centuries, but by the 300s “barbarian” groups like the Goths had encroached beyond the Empire's borders.
D. Higher prices Is the answer
