Although Greek temples are beautiful and impressive the engineering was not advanced. They are dark and windowless brick fortresses. The real change was the highly engineered [flying buttress design](https://i.pinimg.com/736x/21/fd/66/21fd661a0edbd41478e663e52b176a84--ribbed-vault-flying-buttress.jpg) that moves the weight of the roof off the side walls allowing spectacular walls of windows and light.