Originally, the rook symbolized a chariot. The Persian word rokh means chariot, and the corresponding pieces in Oriental chess games such as xiangqi and shogi have names meaning chariot. Persian War Chariots were heavily armoured, carrying a driver and at least one ranged-weapon bearer, such as an archer.

Modern ones are akin to siege towers is my take.

You haven't played enough Stronghold

siege tower.

My take is that they represent a fort, or to put it another way, an engineer Corp. They attack linearly, which makes them bad at offense, but they're powerful field control.

They can't get out early and it's easy to spot their attacks, but their range is fantastic