Baptism and church history

When preparing to teach about the errors in the book “The DaVinci Code” by Dan Brown, I learned that at the time of Constantine (325 AD) the church believed that baptism washed away sin. (sort of Roman Catholic and Lutheran). That is why Constantine didn’t want to get baptized until he was going to die – that way his sins would be washed away w/ the baptism.

The paedo Baptists argue their case from church history. However, as early as the 4th century, the teaching on baptism had been polluted.