Vimanas
The account
The Hindu epics would describe flying machines, and a technical manual would teach how to build them.
What investigators found
The vimanas of the epics are chariots of the gods. The manual, the Vaimanika Shastra, was written in the early 20th century, and a 1974 study by the Indian Institute of Science concluded that the designs would not fly.
The story
India's great epics, such as the Ramayana, describe flying chariots called vimanas. In the most famous episode, the demon king Ravana kidnaps the princess Sita and escapes through the skies in the chariot Pushpaka. For supporters of the ancient astronaut theory, these passages would be memories of real machines.
The theory gained momentum with a supposed technical manual, the Vaimanika Shastra, which includes drawings and instructions for building aircraft. Many present it as a text thousands of years old.
In fact, the manual was dictated in the early 20th century, between 1918 and 1923, by Pandit Subbaraya Shastry, who said he received it through spiritual inspiration. In 1974, engineers at the Indian Institute of Science, in Bangalore, analyzed the designs and concluded that none of them could fly. The vimanas of the epics remain beautiful mythology: chariots of the gods, not pieces of engineering.