The capital of the great Aztec empire, which eventually morphed into today’s Mexico City, had about 300,000 inhabitants when Spanish conquistadors arrived in 1521.
Machu Picchu was constructed around 1450, at the height of the Inca empire, and was abandoned less than 100 years later, as the empire collapsed under Spanish conquest.
The Goths and Vandals make a mess of the Roman Empire next, but the last laugh is on them—most of them will become Romanized, eventually speaking Spanish, Italian and so on.