What is the fine-grained topic of the following text: One cylinder recounted how Nabonidus (reigned 555–539 bc), the father of Belshazzar and the last king of Babylon, had excavated the temple to its original cornerstone, laid 4,200 years earlier by Naram-Sin, the son of King Sargon of Akkad. Only return the topic.
Nabonidus' excavation of Naram-Sin's temple