In ruins, the ruins of a building, city, or other structure that has been destroyed or is in deterioration or decay: We went to see the old Greek ruins. A demolished or decaying structure, town, etc. that remains as evidence of past activity: The ancient Roman ruins are a familiar sight on tour buses traveling through Italy. That's how we know they're ancient. The ancients built their structures to last; today's builders don't put that much effort into their work. You can tell that the Coliseum was built very recently by comparing it to some of the other ruins around it; they're all covered in dirt and some of them have parts missing. The Greeks were the pioneers of architecture who created many beautiful buildings that still stand today. The Romans took what the Greeks had done and added more muscle to these structures. The Christians then had a big influence on modern architecture using lots of gold and marble. After the Muslims conquered southern France in 732 AD, they used whatever materials were available so most buildings during this time period would be made of stone or wood. In the 13th century, castles started to become popular and remain a common sight in Europe today. They're usually built with thick walls to protect their inhabitants from attack. Inside the castle, kings and queens lived in large rooms called salons.