'toe the line' originates from English, specifically the phrase 'toe the mark/line,' where 'toe' meant 'to place the toe against (a line or mark)' and 'line' meant 'a physical line or boundary.'

'toe the line' evolved from earlier phrases such as 'toe the mark' used in the 18th–19th centuries (e.g., at starting lines or military formations) and eventually became the common modern expression 'toe the line.'

Initially it meant 'literally to place one's toes on a line or mark' (for example at a starting line or in formation), but over time it evolved into the figurative meaning 'to conform to rules or authority.'