All 3 Uses of

medieval
in
The House of Hades

He turned a corner and saw two ancient stone towers jutting into the sky, side by side, much taller than anything else in the neighborhood—maybe medieval watchtowers?†
p. 86.6 *

Beyond the main boulevard, the city was a hodgepodge of medieval castle towers, Roman walls, limestone town houses with red-tiled roofs, and modern office buildings all crammed together.†
p. 269.7

Above that sprawled a medieval-looking city of church spires, domes, and tightly wedged buildings, all made of the same golden stone.†
p. 442.4

Definitions:

(1) (medieval)
relating to or belonging to the Middle Ages

(The period of European history beginning with the fall of the Roman Empire and followed by the Renaissance -- roughly 500-1500 AD)

Often thought of as a time of instability, superstition, plagues, feudal lords, and knighthood.
(2) (meaning too rare to warrant focus)
meaning too rare to warrant focus:

Much more rarely, medieval may be used to refer to something as old-fashioned and unenlightened.