I recommend you all to study the Roman Empire, it is the most recent example we have of a lost civilization.

After its fall many techniques and technologies that they used for centuries were lost, some like their cement have not been used again.

The sewage system took centuries to be reintroduced and the same with the lead pipes for water.

Many of Europe's roads have been built on the foundations of Roman roads that have lasted 2 millennia, it is simply incredible.

After the fall of the Roman Empire, Europe fell into centuries of decadence.