The Dark Ages is a period of European history that we know very little about – there is very little written record, and that is why its called the “Dark Ages”. Its supposed to start somewhere around 476 AD and lasted to around to 1000 AD.
Up until the Dark Ages, the Roman empire had conquered and untied Europe in a way that the world has never seen before. There had been written language, philosophy, math, and art for thousands of years. And all of a sudden, it was like technology went backwards thousands of years.
Rome had the aquaducts, sewage and running water. After the Dark Ages started, it was like people forgot how to build stuff like that.
Greece had the arts and science. In the Dark Ages, it was like people were living in the stone age again.