In Iraq, for example, the Americans had this tactic: if a shot was fired somewhere 10 km away, they would immediately fire a shell – BOOM!!! – and then silence...
That's what I meant by "technique."
P.S. Dragon, I'm sorry to disappoint you, but those very barbarians had the same ballistas (and don't tell me they were catapults. Actually, ballistas are stone-throwing machines, and catapults are what you all called ballistas))), plus they mastered new techniques for processing iron and steel, the technique of multi-layer forging, they started using armor, and finally, they had excellent military leaders, while the Romans had recently lost their best general...
Added 2 minutes later
Sever, by the way, it's not necessarily true that if there are many people, there is a lot of equipment – I'm saying, it's all about quality!)) You can, for example, set up a factory where 500 people work and produce 1 tank in 5 days (FOR EXAMPLE!), or you can create an automated workshop where 5 people work and produce a tank in 3 days. Which is more profitable and better?))