You have a big Venetian city, oops, sorry I thought it was Venice because it's totally flat and crisscrossed with canals. Rome, you say? OK you have a big Roman city attacked by elephants and catapults. Since you have no watch towers you never saw the elephants standing 5 feet outside your walls. Who could see something that small approaching? Having no map of your own city, you have no idea what the countryside looks like a mile away. Having no generals -- in Rome (??!!) you have positioned your archers and foot soldiers in all the wrong places. Maybe you really shouldn't be in the city business at all.