Beneath Thy Protection (Ancient Greek: Ὑπὸ τὴν σὴν εὐσπλαγχνίαν; Latin: Sub Tuum Præsidium) is an ancient Christian hymn and prayer. It is one of the oldest known Marian prayers and among the most ancient preserved hymns to the Blessed Virgin Mary that is still in use. Papyrus 470, containing a substantial portion of the prayer, was dated initially to the 3rd or 4th century; however later scholars proposed much later datings, even as far as the 9th century.
en.wikipedia.org
The hymn in question agrees with Orthodox doctrine, and I would also note that the Orthodox do not accept the doctrine of the Immaculate Conception, although we would not need to since our understanding of original sin is not that of St. Augustine of Hippo but rather of St. John Cassian.
Specifically the Immaculate Conception is based on the Augustinian idea that original sin is spread through concupiscience and thus all actions of sexual intercourse spread original disease, which requires an exception to be carved out for the Blessed Virgin Mary. The view of the Orthodox is simply that original sin is spread otherwise (we also refer to it as ancestral sin) and thus we do not require a separate doctrine to explain the sinlessness of the virgin Mary.
At any rate even if the hymn in question dated from the ninth century, which I strongly doubt, that would be irrelevant since the words it contains reflect the teachings of the Eastern Orthodox and the Oriental Orthodox, and the Oriental Orthodox in particular were pushed out of Eucharistic communion with Rome and the Eastern Orthodox by the writings of Pope Leo I and their endorsement at the Council of Chalcedon, insofar as they appeared to potentially contradict the teaching of St. Cyril of Alexandria and be a reversion to the Nestorian position (I would argue that Chalcedonianism is not Nestorian, but I understand why it alarmed the Oriental Orthodox and I regard the Oriental Orthodox as being the most stalwart defenders of the ancient faith).’
Since their doctrine agrees with the hymn in question, this means that the doctrine the hymn refers to is definitely ancient and apostolic, and furthermore it also means that an early dating for the hymn, for example, to the fourth or even the third century, is entirely possible and even likely.
I would say, since its a Latin hymn, it most likely originates around the year 400, since most of the particularly beautiful Latin hymns were composed following the introduction of antiphonal singing into the Church of Milan by St. Ambrose in 386 AD, or else originated in North Africa or in places in the Western Church other than Rome. Rome itself was not a hotbed for hymnography until the late fifth century when it began to catch up in this area. However, there are some very beautiful hymns in Latin from before that time.
There are also other Mariological hymns of greater antiquity.