Both Uses of

medieval
in
The Hidden Oracle

If it were possible to run from disease spirits, the medieval Europeans would've put on their track shoes and escaped the Black Death.†
p. 58.4 *

It could have been a modest abode in almost any age—ancient Athens, medieval France, the farmlands of Iowa.†
p. 83.1

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.