Space 1889: Martian Gun Towers

These drawings by Jeffrey Chew of 19th-century colonial fortifications, so called Martellos, are easily adapted to the peculiarities of Martian warfare, primarily by the addition of machine guns or pompoms that are supposed to engage airborne foes. After all, raids by High Martians are uncomfortably common at outlying garrisons that guard mountain passes or caravan routes.

On Venus, one would find these towers next to trading posts and ports.