[Andrew_nenakhov]

Gp was talking about scientific discoveries, and of those none were lost. Aristotle didn't make any discoveries, he just had some ideas, which were totally useless in the medieval Europe. That uselessness is the reason they were lost: simply nobody cared to preserve them. Metalworking, hydraulics of the time, building methods were all very useful and were preserved. The only 'lost' technology is probably Roman concrete, which required some highly specific ingredient. But that's about it.

[qwytw]

There was a significant decline in certain areas at least in Western Europe both in building methods and metalworking based on archeological evidence. After urban populations collapsed there simple was no demand for large complex buildings, metal statues etc. Of course most the knowledge was preserved in the part of the Roman empire that survived and in other pockets and by the high middle ages Europe had well surpassed it's Roman high economically and technologically.

[allturtles]

You're conflating scientific knowledge and the practical arts. There is lots of scientific knowledge in Aristotle and the other authors I mentioned. e.g. Aristotle's physics. We would now consider it wrong, but those who rediscovered it didn't think so.

Even in the category of practical arts, though, you're mistaken. Check out the writings of Hero of Alexandria or Vitriuvius. Check out the waterwheels at Barbegal. Pick any major civil engineering project like the aqueducts, baths, roads, or arenas of ancient Rome. There is no equivalent until the cathedrals of the later middle ages.

[Andrew_nenakhov]

There is no equivalent only because there were no economy that could afford such projects. Kingdoms were much smaller and couldn't waste resources on grandiose vanity projects. People certainly knew how to make an aqueduct, or a road.

As for arenas, they came out of fashion with the rise of the Christianity. You know, publicly feeding early Christians to lions didn't help popularize this type of entertainment.

Also, all this knowledge was very well alive in Constantinople, so any rich ruler who wanted to build a replica of Hagia Sofia could just hire someone from there. The only problem, there weren't any such rulers who had enough resources.

Regarding Barbegal waterwheels, what do you suggest checking? Waterwheels were abundant in all medieval Europe, this knowledge was never lost.