When you dig tunels you can find some ruines, artefacts and old monuments. After completing dig'em up you can claim these for unloking some levels or to gain some skills.
I mean to find ruins and monuments to claim for upgrading some skills or levels! Not for personal use. If you dig a tunel and find an ancient sword you can use it as a sacrifice to increase your monument radius. Or if you find a ruin of an ancient stone building after you complete dig it up you can claim on this to increase your combat skills.
old roman armor ? after a century under the soil, any metal become unusable... here you'd like to use an armor that at least stayed in earth for 500 years.... ?