When somebody is told to toe the line, they are expected to follow the rules and submit to authority. Originally this phrase refers to the lines drawn along the two front benches in the House of Commons which still exists. The two lines are strategically placed at a distance far enough apart to prevent opposing members reaching each other with their swords, should the debating become heated enough. Any member becoming animated enough during an argument to step over a line would be called to order and told to ‘toe the line’. Tradition still prevents members from ‘crossing the line’ but sadly these days none of them are allowed to carry swords or other weapons, although it would be far more fun if they did.