Eleven skulls of Homo erectus were found on a river terrace of the Solo River at the small village of Ngandong in 1931.

Reported by von Koenigswald, the interpretation of this site is still hotly debated. Not only are the fossils highly evolved (implying a young age), the large number of skulls have suggested to some workers that they might represent an ancient sacrifice.  Less excitingly, the skulls may have been reworked from older deposits upstream of Ngandong.

The dating of associated material suggests they may be as young as 27,000 years which would make them the youngest Homo erectus to have survived anywhere in the world; the most recent fossils of this species in Africa are a lot older at around 900,000 years.