If you do an internet search of “castles for sale,” you’ll always find an array of beautiful stone houses, mostly in France. Most of them are “chateaux,” that is, the word “castle” updated into modern French. As the word changed, so did the building. A chateau is usually made of stone, but otherwise it’s just a large mansion.
People continued to built real castles, but their concerns had changed. Once battles were fought in the field, defending the house itself mattered much less again. And when a battle was fought for the house, fire was a chief concern. The 13th century fighting machines generally had wooden roof structures and sometimes wooden shingles. Many interior parts were made of wood, especially the interior subflooring. When the timbers caught fire, the stones heated and cracked. Some stone held up better to fire, some worse; if the stone block had a pocket of some mineral impurity, it might heat more rapidly and burst the stone.
So if you wanted a fire-proof castle, brick was the way to go. Bricks cost much less, being locally produced. You didn’t have to ship big blocks of stone down a river or drag them from a quarry. You could set up a brickworks very near the site and have your own clay kilned as it was dug from the foundation. Bricks took a long time to make properly, but once cooled, they were impervious to fire. So were roof tiles, made by the same brickworks. A chateau made of brick, with a tile roof and glass windows, was probably a better bet for artillery defense.
Some of the new castles were still made with round towers and moats. They certainly still focused on thick, strong doors. But the old death trap gatehouses were pointless unless they were part of a dedicated military structure. By contrast, some castles ceased to be residences and turned into true forts. Mont Orgeuil, on Jersey Island, was reinforced by extra layers of stone during Tudor times. The stone now had to absorb artillery fire. The castle’s towers were topped with artillery, too. Arrow slits became gun slits, rebuilt to fit the new round barrels.
In the castle houses, the chateaux, round and square corner towers began to have bedrooms as well as staircases. Parapets on top of the towers gave over to tiled roofs. You can still see the castle-like outline in a chateau, but the peaked towers standing higher than the rest of the house no longer have any defensive function. The round towers are for style, not to see around corners. Thick walls are for insulation, not for defense; window seats are for comfort, not for archers.