Numbers 7:9

But unto the sons of Kohath he gave none ,.... Being all disposed of to the sons of Gershon and Merari: the reason of which follows:

because the service of the sanctuary belonging unto them was that they should bear upon their shoulders ; as the ark with the mercy seat, and cherubim, the shewbread table, the candlestick, and the two altars; though in later times we find the ark was sometimes not only carried by the priests, but upon a cart, Joshua 3:17 .