Despite being awesome marvels and once incredibly important, ever since explosives became a thing, castles have become obsolete. Until now...
Imagine two equally advanced civilizations at war. Both factions feel as if castles make great forts in that day of age (futuristic scifi).
These castles externally appear as if they are medieval castles but are also armed with higher degrees of defense mechanisms such as force fields and anti-aircraft turrets. They use the castles to hold weaponry and supplies, house troops, and to hold strategic defensive locations.
The civilizations don't use exclusively castles but I would say that about 33% of each faction's forts are castles.
Why would civilizations with advanced technology (think Star Wars-like technology) even consider using castles as forts?