Network switch or a firewall?

I have a distributed network. The government mandates we have a 6 wall security around the network. Because we have a distrubuted system we will have many protected sites within a network. Because there are wires connecting each site someone could cut into a wire and get to either location. We have to put a switch or a firewall at each end of the wire. We do have to maintain strong security and logging to detect for incidents.