Mining in Roman Britain was when people went underground into the earth to find valuable rocks and minerals.
Imagine if you were playing with sand in the park, and you found a shiny rock that you really loved. Now imagine if you went on a treasure hunt, looking for lots of those shiny rocks. Romans did this on a much larger scale, looking for things like tin, lead, and gold.
The Romans had tools like hammers, pickaxes, and shovels to help them mine. They would first dig a big hole in the ground called a "shaft" and then dig tunnels called "galleries" leading off from it. In these galleries, they would look for veins of valuable minerals and then dig them out.
Mining was really hard work, as you had to dig deep into the ground and work in the dark with just torches for light. It was also really dangerous, as tunnels could collapse on miners, or they could run into poisonous gases.
But mining was really important, as the valuable minerals they found were used to make things like weapons, coins, and jewelry. Without mining, the Romans wouldn't have been able to make as many things and would have been weaker as a society.