Infant Baptism?

Baptize means to submerge, dip, or immerse, which is why sprinkling isn't really baptism.  As for ritual washings, there are indeed many religions which do this, but for different reasons.

For the Jews the ritual washings go back to Leviticus 1:4, 24 when the priest bathed before doing his temple duties.  In the century or so before Christ, Jews began a heavy emphasis on ritual washings to cleanse from impurity.  Somewhere along the line they began the ritual bathing — baptizing — of Gentile converts (although I guess circumcision was still done).  John the baptist did the ritual for people who repented of their sins — had a change of heart about their lives and wanted to be devoted to following God.  Baptism was a sign of identity with the group holding to the particular belief.  So when Jesus said to be baptized, it was for the same reason as John's baptism, except the baptized person's identity was now with Christ. (1 Cor. 6:11)

The Bible tells us our baptism is symbolic of our death, burial, and resurrection in Christ, which is why immersion is important.  Without the actual immersion the symbolism is lost.  Acts 8:38-39 says they went down into and came up out of the water, which demonstrates the method used.  See also Rom. 6:3-11, Col. 2:11-12.  

The Didache (written before 100 AD) said that baptism should be in running water (river, stream, e.g.), and if not available, then in other water (pond, e.g.).  Preferably cold water if available.  If running or standing water for immersing isn't available, then and only then would you pour water on the head three times. 

So when did it turn to sprinkling? The writings of Justin Martyr (c.100-165) tell of immersion. The Didache says that there should be no question of baptizing children because baptism is only for "convinced and determined" believers.  Tertullian (C.150-212 AD), also described baptism as by immersion.  It appears, from the various references in my library, that immersion didn't get supplanted until towards the end of the 2nd century when the papacy began coming into power. By 250 AD (my best guess from the ambiguity of some of the dates) the idea of infant baptism came about as a sacrament rather than as a symbol. Infant baptism was when they started using "Christian" names, while previously you kept your old "pagan" name and just called yourself a Christian. 

So apparently changing to sprinkling wasn't for Roman political reasons — it was for Roman papacy reasons. It appears that immersion continued as late as at least 300 AD while being supplanted by infant baptism.  (Of course there were those sects who always fought infant baptism and the papacy in general, and were persecuted and virtually wiped out for defying the Pope.)