I was struck by the beauty of Forte Spagnolo in L'Aquila[1].

The purpose of most star forts appears to be keeping a city safe from armies. Forte Spagnolo was built to keep an army safe from a city! Are there any other forts where this is the case?

[1] https://en.wikipedia.org/wiki/Forte_Spagnolo,_L%27Aquila

The Tower of London arguably qualifies as a fort built to protect its inhabitants from the city. In its original form, its most impressive and formidable defenses faced London.