I read recently that glass is five times stronger than steel, and its brittleness is because of impurities and flaws caused by the manufacturing process. With modern manufacturing techniques we can remove those and make glass the perfect construction material.
Jury's still out on that one, but I'll be interested to see where it goes.
It probably depends on the definition of stronger. Concrete is stronger in compression. If weight ratios are used then glass could win due to being lighter.
I heard this one recently from the person leading a historical tour. I looked around and everyone in the group was just nodding like, "oh, how interesting!"