When you think Rome, you think the Colosseum. It's one of the great structures of the Roman Empire, and it still dominates the landscape of the modern city. But how deep does your knowledge of the Colosseum actually go? Which emperor built the Amphitheatrum Flavium (as it was originally called)? For what purpose? And how, stylistically, was it originally built and decorated? All of this gets answered in an image-packed lecture by Yale professor Diana E.E. Kleiner, which forms part of her larger course on Roman Architecture. (Find it on YouTube, iTunes and Yale's Open Course web site). I queued up the lecture at the 20 minute, when Kleiner starts talking about the Colosseum itself. But you can move back to the very beginning if you want to get some more political context.
Finally, let me mention that Google also lets you revisit Ancient Rome. Google Earth offers a nice 3D view of the Colosseum and other important Roman monuments, while Google Street View you tour the ancient ruins of Pompeii. It's all free, of course.