Jewels of 90 years

Years ago in Saudi Arabia, an order came to dig for groundwater. What was discovered was a big surprise. Black gold quickly changed the Kingdom's livelihood. But somethings didn't change at all, such as the love of their culture that Saudis felt and their connection to the wild desert. 
A historian is waiting for us in the Ithra Library, ready to enrich us with an important milestone for the Kingdom that we might not know about. Can you guess what it could be?