Around the time of the Spanish Inquisition and the Black Plague (and the practice of last names coming into vogue), the pressure built up by the Sundering finally broke, causing the Shattering (prompting large numbers of Fae to either jump ship for Arcadia or adopt the Changeling Way, or hide). Between 1200-1400 AD and 1500-1600 AD, the breaking away of the mythic from the mundane became more complete. The pathway trods between the Mundane world and the Dreamings began to vanish and/or close, as did the routes leading to Arcadia.
Eventually the threads that were pulled so thin between the mortal realm and the Dreaming began to snap. This severing is the Shattering. Not only did it shatter the ties between Arcadia the Earth but the hopes that it could be reversed.
While the word 'Shattering' calls to mind a cataclysmic event, it was actually a process of small catastrophes as the portal began to get brittle and crumble; sealing off access to the Dreaming. Some point to the Black Plague in 1347 as the great catalyst. Between 1347 and 1352 over 75 million people died in Europe. The wave of fear and horror echoed across the Mists, throughout the Dreaming and even to Arcadia.
The 14th century brought the advent of Reason and Science which did their best to end the rest of the beliefs in the mysterious and uncontrollable. Common people took refuge in religion and particularly the comfort the Church could give over the old ways; a church which had no use for any magic but its own.
As the portals continued to shatter, every faerie had to make one of three choices. Some fled to their places of power and sealed them off from the world, becoming known as the Lost Ones. It is believed many of them still survive, lost in their own unchanging worlds.
Most of the Sidhe, with a handful of exceptions like House Scathach, fled to Arcadia. Pitched battles were fought at the trods as frantic nobles sought to get through before the crumbled completely. When Silver's Gate at the Court of All Kings fell, the last of them, it was truly the end of the age.
Abandoned by the nobles, the Commoner kith were trapped and sought to adapt themselves to the cold world of Banality they found themselves forced to endure. Covering themselves with veneers of Banality to protect their fragile selves, the Changeling Way was born. This half-life for the fae continued for the next six centuries in the time known as the Interregnum.