The distance from the earth to the firmament is five hundred years' journey, and so it is from each successive firmament to the next, throughout the series of the seven heavens.
P'sachim, fol. 94, col. 2.
"Now, as I beheld the living creatures, behold, one wheel upon the earth by the living creatures" (Ezek. i. 15). Rabbi Elazar says it was an angel who stood upon the earth, and his head reached to the living creatures. It is recorded in a Mishna that his name is Sandalphon, who towers above his fellow-angels to a height of five hundred years' journey; he stands behind the chariot and binds crowns on the head of his Creator.
Chaggigah, fol. 13, col. 2.
In the Liturgy for the Feast of Tabernacles it is said that Sandalphon gathers in his hands the prayers of Israel, and, forming a wreath of them, he adjures it to ascend as an orb for the head of the supreme King of kings.
The mount of the Temple was five hundred yards square.
Middoth, chap. 2.