Gameplay: make rivers, which reach the sea, navigable - valid terrain for ships. In combat, they can move only on river tiles.
Bonus: let cities on rivers build ships and merchant guilds.
Double bonus: redefine lakes connected to seas by rivers as inner seas, or just sea for simplicity, and let them be navigable/merchant guild.
Bonus: let cities on rivers build ships and merchant guilds.
Double bonus: redefine lakes connected to seas by rivers as inner seas, or just sea for simplicity, and let them be navigable/merchant guild.
