The Three Assemblies

[T]he place where the Sutra is delivered will be changed at the beginning of the next chapter. Up to and including this chapter, the Buddha has been speaking on Mount Sacred Eagle, near the city of Rajagriha. After a mysterious phenomenon takes place at the beginning of Chapter Eleven, and continuing until Chapter Twenty-two, his sermon will be delivered around a treasure tower (stupa) which is hanging in space. Since that part of the sutra is delivered from this new location, the section from Chapters Eleven to Twenty-two is referred to as the “Assembly in Space,” or “Assembly in the Sky.” The scenes before and after the assembly in the sky are called respectively, the “First Assembly on Mt. Sacred Eagle” and “Second Assembly on Mt. Sacred Eagle.”

Introduction to the Lotus Sutra