For me it is what they achieved to do . Much of it was breaking new ground , never been done before . Tools were very basic , getting levels , angles and vertical was done using a plumb Bob . Someone even had to invent the principle of it ,build a tool that allowed levels , angles and verticals to be used .
Today’s modern tooling is based a great deal on those early principles , our knowledge is based on what they handed down over centuries even millennia in a lot of construction .
The Romans gave us concrete , arches , aqueducts , roof tiles , ceramic tiles , arenas , straight roads and road building techniques . The Greeks gave us columns and pillars, and maybe glass . The Normans high buildings, domes etc . When you look at the great wall of China, the pyramids , the Roman coliseums , the Norman cathedrals and castles , they are all marvels of construction , have stood for millenia and you have to admire their workmanship and skill and the knowledge and ideas we today take for granted , and of which we may not of had were it not for those pioneers .