Geography of Rome and Constantinople

Constantinople
http://www.historynet.com/ancient-history-walls-of-constantinople.htm

http://neobyzantium.com/why-constantinople-was-so-hard-to-conquer/

http://www.kidspast.com/world-history/0143-constantinople.php

Rome

http://www.mw.k12.ny.us/webpages/jahearn/files/geography_of_ancient_rome0001.pdf

http://www.mariamilani.com/ancient_rome/Ancient%20Rome%20Geography_.htm