[Region 1][Map 25][Location 4] - Port Magalie

[Gandwarf]

There is one possibility from Robert Jordan's Wheel of Time novels--a particular city's harbors are defended by chains that normally lie on the river bottom. If the city is threatened, they are winched up to just above the water-line. That seems a pretty flimsy defense to me, though. Any enemy who knows it's there would simply attack it with a heavy ramming ship and likely rip the chain right out of its mechanism.

Chains have been used a lot here in Europe, mainly to block traffic on the rivers (mostly to collect toll). This is a nice read:

http://www.ricksteves.com/tvr/pledge...chap_rhine.htm

It gives some information on Rhine castles, mostly built by robber barons
They had the castle on one of the banks and a tower on the other bank. A chain was between them and could be raised.
Also see:
http://en.wikipedia.org/wiki/Robber_baron

It seems the robber barons were put out of business when their castles were destroyed one after the other