This was a peaceful time period during the prehistoric age when the Moon Kingdom existed, along with the rest of the Solar System. It provides a setting for the past lives and future selves in Crystal Tokyo. The Silver Millennium functions as a major driving force behind both plot and characterization. The original Silver Millennium is portrayed as an ancient Golden Age, marked by peace, prosperity, and good relations between the people of Earth and Moon. Despite its name, the Silver Millennium appears to have lasted much longer than a thousand years.
It was also time, when Queen Serenity, Princess Serenity, Prince Endymion and their respective guardians lived. When Endymion fell in love with Serenity, Beryl made rebellion of Earth people and finally, the war between Beryl and Moon ended the era of Silver Millennium.
The lifespan of the Silver Millennium family is about 1000 years. The rate of aging halts after adulthood due to the power of the Silver Crystal. After King Endymion and Neo Queen Serenity took the throne in the 21st century an era of long life begun in Crystal Tokyo. Now nearly everyone on Earth has gained humanity's greatest wish, long life.