Structure III isn’t the largest building at Calakmul, and it was likely never the fanciest, but it’s by far the most interesting one there:
It was typical in the Maya Classic era to periodically rebuild structures — tearing down old superstructures, covering their platforms with another layer of masonry, building anew on top of them. In some cases, this happened every 20 or 50 years for centuries — that’s why a number of them took on elephantine proportions.
Structure III was different, though. It seems to have been inhabited for the duration of Calakmul’s existence (about 1,500 years), but was never buried and rebuilt. Fairly early in its history, a very well-appointed tomb was built into one of its rear rooms — other than that, it appears that nothing was done to alter its original architecture.
For 1,500 years.
The inhabitants did such a good job of maintenance that when Calakmul was rediscovered 1,000 years after it was abandoned, this was the only structure at the site that wasn’t just a rubble mound. It’s thought that the tomb held one of the original kings of the site, and that Structure III was a palace inhabited by his descendants.