I'm a newbie for BTS (not entirely since I managed to win in noble level). But I have a maybe minor but serious question about the city/resource connection by river. I'm playing BTS 3.19. My question is: Why my two cities can be connected without "sailing" tech? Please see attached screenshots and the save file. The second city York is connected to the capital. But I haven't researched the "sailing" tech. And according to the description of "sailing", it enables the connection through river. It maybe a minor problem, but sometimes, this will affect the order of tech I should research. For example, two cities are nearby river, one city is sitting on an important resource, then I don't need to research road, or even "sailing" to enable to connection? Thanks for you attention and help.