An ancient battle has driven a wetland species almost to extinction

Then everything changed when the Fire Nation—sorry, the Han Empire—attacked.

Han rose to power in the wake of Qin’s collapse, after a short war with a rival dynasty called Chu, and spent the next century smugly referring to Nanyue as a vassal state and occasionally demanding tribute. At times, the rulers of Nanyue played along, but it all came to a head around 111 BCE, in the wake of an attempted coup and a series of assassinations. The Han Emperor sent an army of between 100,000 and 200,000 soldiers to invade Nanyue under a general named Lu Bode.

The troops marched across the countryside from five directions, converging outside Nanyue’s capital city of Panyou, which stood in the Pearl River Delta, near the modern city of Guangzhou. An enterprising company commander named Yang Pu got the bright idea to set the city on fire, and it ended badly.

“The fire not only destroyed the city but also ran out of control to the surrounding forests,” write Wang and colleagues. The cypress trees burned down to the waterline, leaving only their submerged stumps behind.

After war came fire and rice

At the time of the invasion, the land around Panyou was mostly swamp, forested with cypress trees. People had lived there for thousands of years, and had been growing rice for about 2,000 years. Bits of charcoal in the peat layers Wang and colleagues sampled reveal that they practiced slash-and-burn agriculture, but on a small scale, rotating their fields so the cypress forest could start to recover after a season or two.

The small burns are nothing like the forest fire Yang Pu unleashed, or the massive burning and reworking of the landscape that came after.

The stumps of the burned cypress trees slowly disappeared under several meters of peat, while above the buried ancient forest, life went on. Tigers, elephants, rhinos, and green peafowl no longer walked here. Instead, grains of pollen from the layers of clay above the peat reveal a sudden influx of plants from the grassy Poaceae family, which includes rice, wheat, and barley.