Well, they had many secrets, since in this type of construction they applied the so-called Sacred Geometry, so everything had a very special symbolism. Unlike today, those medieval stonemasons were craftsmen, as they were from other guilds: carpenters, silversmiths, blacksmiths, etc. and they did their work conscientiously. Now it is built piecemeal, not with those hard stone materials, but with materials that are lighter and therefore less durable. Thanks for your comment