not on subject for ... the answers, but

IMO the landbridges become essential for the computer ai to act rationally and effectively. the ai becomes landlocked often in the 1st medieval game if the bridges are removed. it has some trouble getting crusades to move to the orient across constantiople if there isn't a bridge. i remember many times even in rome total war the scippi and brutti would not act well with their fleets. they would not take advantage of their fleet advantages and they would not do seabourne invasions in any concrete way. many times i saw the brutti move armies up the peninsula of italy and back down the balkan side instead of just ferrying the army straight across to greece.