The Pyramids of Giza stand out from the other wonders on the list in both age and size. Built at least 4500 years ago it is almost 2000 years older than every other traditional wonder, and twice as old as the Lighthouse of Alexandria and the Colossus of Rhodes. The base of the largest pyramid, which is attributed to the Egyptian King Khufu, measures 230 meters by 230 meters and is large enough to fit 8 temples of Artemis with room to spare. The Great Pyramid was also the tallest building in the world for 3800 years after it was built, standing origionally at 147 meters tall. Most historians believe the pyramids were built as tombs for the Pharohs, though it appears they have all been looted long ago. Due to the fact that no artifacts or writing was found inside the pyramids many have specualted on alternative interpretations for its age and function. Recently a remote scan of the great pyramid has revealed a hollow space which some believe is a hidden room located near the Grand Gallery of the Pyramid. Hopefully this can turn out to be a great discovery and lead to more answers to the never ending questions this ancient monument poses.
Picture from ancientworldwonders.com