fieri facias

The story

1. Medieval Latin · derived fromfierī faciās“thou shouldst cause it to be done”
2. Middle English · inherited fromfieri facias
3. English todayfieri facias

From Middle English fieri facias, from Medieval Latin fierī faciās (“thou shouldst cause it to be done”), which is not a normal Classical Latin construction but a calque from Romance causatives from faciō and infinitive (attested since Late Latin).