James E. Talmage,
The House of the Lord: A Study of Holy Sanctuaries Ancient and Modern
“ The placing of the baptistry on the lower or basement floor was not a matter of mere convenience. Most of the baptisms performed within the Temple are in behalf of the dead, and the symbolism of the font location is set forth by authority:"The baptismal font was instituted as a simile of the grave, and was commanded to be in a place underneath where the living are wont to assemble, to show forth the living and the dead." ”
