Rafael Solano/Jane Villanueva; Jane Villanueva; Rafael Solano; Sex Toys; Romance; One Shot; Light Dom/sub; Vibrators; Cute; classic jafael bickering; now with sex! Summary (Post Chapter Seventy-Four, S4E10) Jane and Rafael's relationship is going along swimmingly until Jane accidentally pulls an Alba.
The Dark Ages is a categorization commonly used to describe the period between the fall of the Roman Empire and the beginning of the Italian Renaissance and the Age of Exploration. Roughly speaking, the Dark Ages corresponds to the Middle Ages, or from 500 to 1500 AD.
Thus, the answer to the question as asked is, no, Christianity did not cause any dark ages, and the Middle Ages (a more accurate description of the time from Constantine to the Renaissance/Reformation) was a time of complex factors.