The Cyrus Cylinder, discovered in 1879 in the ruins of Babylon, is a clay cylinder inscribed with a declaration by Cyrus the Great of Persia after his conquest of Babylon in 539 BC. The inscription describes Cyrus' policy of allowing displaced peoples to return to their homelands and restore their temples.
This policy is precisely what the Bible describes in 2 Chronicles 36:22-23 and Ezra 1:1-4, where Cyrus issues a decree permitting the Jewish exiles to return to Jerusalem and rebuild the Temple. The Cylinder provides independent confirmation that Cyrus had a general policy of repatriation, making the biblical account historically plausible.
What makes this particularly remarkable is that the prophet Isaiah named Cyrus by name approximately 150 years before his birth (Isaiah 44:28-45:1), calling him God's 'anointed' (mashiach) who would rebuild Jerusalem and set the exiles free. Critics have argued that this portion of Isaiah must have been written after the fact (the Deutero-Isaiah hypothesis), but conservative scholars note that the Dead Sea Scrolls contain a complete Isaiah scroll with no break or change in style at chapter 40.
The Cyrus Cylinder is currently housed in the British Museum.