We report on an elementary quantum network of two atomic ions separated by 230 m. The ions are trapped in different buildings and connected with 520(2) m of optical fiber. At each network node, the electronic state of an ion is entangled with the polarization state of a single cavity photon; subsequent to interference of the photons at a beamsplitter, photon detection heralds entanglement between the two ions. Fidelities of up to (88.2+2.3−6.0)% are achieved with respect to a maximally entangled Bell state, with a success probability of 4×10−5. We analyze the routes to improve these metrics, paving the way for long-distance networks of entangled quantum processors