Memorare
The Memorare has been attributed to St Bernard of Clairvaux, but Wikipedia says that he is probably not the author of the prayer. 15th century, 17th century, 19th century.
The phrase sub tuum praesidium, "under your protection," apparently dates to the 3rd century (!).
O piissima Virgo Maria,
non esse auditum a saeculo,
quemquam ad tua currentem praesidia,
tua implorantem auxilia,
tua petentem suffragia,
esse derelictum.
Ego tali animatus confidentia,
ad te, Virgo Virginum, Mater, curro,
ad te venio,
coram te gemens peccator assisto.
Noli, Mater Verbi, verba mea despicere;
sed audi propitia et exaudi.
Amen.[1]