Ancient extraterrestrial civilizations, millions of years older than humanity, would need enormous amounts of energy.
By creating a swarm of satellites in a spherical shell, they could harness much of the power of their star.
Science fiction author Olaf Stapledon described spherical, energy-trapping alien structures in his 1937 novel "Star Maker":
"Not only was every solar system now surrounded by a gauze of light traps, which focused the escaping solar energy for intelligent use, so that the whole galaxy was dimmed, but many stars that were not suited to be suns were disintegrated, and rifled of their prodigious stores of sub-atomic energy."
Incredible Technology: How to Search for Advanced Alien Civilizations
Recalling Stapledon's description, physicist Freeman Dyson proposed similar structures in a scientific paper in 1960. Dyson realized that alien civilizations could be recognized by their waste heat, which would be detectable as infrared radiation. Dyson proposed that really advanced civilizations would re-engineer their solar systems, perhaps dismantling planets to form a shell of satellites around their star to capture its energy.