The Romans observed the 1st and 2nd century Christains as being a superstitious group of people who placed Jesus before other Gods.
They were viewed as being rather "simple" folk who met in private homes where they sang songs together in praise of Christ and ate basic foods.
This eating of basic foods possibly caused problems with merchants, as it is suggested that in certain areas where Christians refused sacrificial offerings, trade was being affected and the authorities were made aware of this!
Jesus was defined as a magician and a rumour went around Rome suggesting that he had learnt his skills in Egypt, amongst the magic practitioners there.
This accusation was serious, as the practise of magic was outlawed within the Roman Empire and this slur against Jesus would affect the early Christian groups; meaning the Empire would view them with suspicion.
From what I have read, I concur with the other thoughts. There is no evidence that the early Christian Church conducted a regimented preaching work on a door to door basis.
From what I know of the Romans, as tolerant as they were, I cannot see how they would have tolerated this particular intrusion.
I believe the faith would have been more word of mouth and discreet.
Obviously a Christian believes in the invisible reality of God and therefore "nobody comes to the Son, unless the father draws him" (you know the scripture). That is an invisible mechanism and suggests supernatural involvement.
A declaration of faith may be necessary on a personal level, but even the stones would cry out, wouldn't they
Erm... I'm off anyway, hope some of that helps!