TIL about this term's origins!

> act of "toeing the line," most likely from a combination of nautical discipline and athletic races. In the Royal Navy, sailors had to stand with their toes against a line on the deck for inspection, while in sports, runners line up with their toes at the starting line

And while I'm here I'll mention a couple other terms I never knew about:

Slave:

> The English word "slave" originates from the word "Slav," which was used in Medieval Latin (\(<<!nav>>sclavus<<!/nav>>\)) to refer to people of Slavic origin who were frequently captured and sold into slavery during the early Middle Ages.

Pothole:

> A (potentially legendary) origin story suggests the name came from potters digging clay from roads, creating the holes

Yes, the metaphor here is that of perhaps a military officer drawing a line and soldiers are expected to stand along the line, so their toes will touch the line. It's about obedience.

Early examples are clearly about standing in an orderly formation, and also sometimes use alternative words such as "mark" instead of "line" - which wouldn't make sense for tow. You could tow a line, but it's unclear how one might tow a mark.