首楞嚴義疏注經 6.46

6.46

四天王者，上升之元首，下界之初天，於須彌山各居一埵，所領鬼神每王二部，共八部眾，救護國界。

The Four Heavenly Kings are the foremost of ascending [realms] and the first heaven of the lower realm; they each reside on one ledge of Mount Sumeru. As for the ghosts and spirits they command, each king has two divisions, making eight classes of beings in total, who rescue and protect the borders of the realms.