Virgin birth was a part of many stories long before the Christian version came along as many others here have mentioned.
The entire story of Jesus was told numerous times before, over hundreds of years, with all of the elements from birth to death to rising again with the only real differences being the names and places. It was inscribed, if my memory is correct, on a temple wall in Egypt which might well have been heard by travelers from Rome and elsewhere. I want to say it was the temple of Izor but it has been a long time since I read about it and my aged memory isn’t all that good.
In the times of Jesus there were many women claiming to have been impregnated by gods, it was actually rather common. Some were no doubt delusional and others trying to explain away pregnancies that couldn't have been from spouses who were away at the required time.
The “Immaculate Inception” is often credited to a French girl named Bernadette who supposedly heard it from an angel by a spring. Or at least that was the fable.