Fuerte San Jerónimo, closer to Portobelo center, was the largest fortress ever built to protect the bay. Eighteen cannon embrasures face the mouth of the bay, some exactly where the Spanish troops left them in 1821, the year Panama declared independence. Beyond the impressive gateway of San Jerónimo are the remains of the officers’ quarters, barracks and a guardroom.
If you’re short on time, San Jerónimo is more complete and makes for a better visit than Fuerte Santiago.