I'm researching constructing bridges in order to create an entrance large enough for a caravan to get to a trade depot, but also defensible in case of an attack.
http://dwarffortresswiki.org/index.php/DF2014:Bridge#Raising_and_retracting_bridges
Drawbridges are terrifying. #dwarffortress https://tootplanet.space/media/9gMPVKK7Mvku_lY6JKw