Help identify these roots I found in my garden?

I was digging around and found a network of roots with peanut-like things attached to them. Instead of peanuts, these weird little pods have the consistency of water chestnuts if you snap them open. They cluster around the roots in groups. So odd, as there are no longer any plants associated with these things above ground—they’re at least two years old because I planted tomatoes in this area last year.