In 1977, Heyerdahl led the construction of his largest reed vessel—18 meters long—where the rivers Euphrates and Tigris flow together in the former Mesopotamia. The boat was named Tigris. They started the voyage from the river Shatt al-Arab in Iraq. The Tigris then continued down the Persian Gulf and out into the Arabian Sea.

One autumn day in 1982, Thor Heyerdahl received a letter in the post. The envelope contained a photograph of a hitherto unknown stone statue from the island kingdom of the Maldives in the Indian Ocean. It enticed him to launch an archaeological expedition, to find out more about those who had made the statue in the photograph.

In the period 1988–1992, Thor Heyerdahl led archaeological excavations of the pyramid complex "La Raya" in Peru. In the area there were 26 pyramid-like constructions of sun-dried clay, so-called adobe blocks. The archaeologists concluded that the ruined city outside Túcume was built around 1100 AD.