I don't know if there were any religious wars prior to the middle ages, I just can't think of any. At least not any that were sold that way, to destroy the enemy because he worshipped the wrong gods. Even the wars mentioned in the Old Testament were not fought for strictly religious reasons.

As for the future of a Roman timeline, who knows where they might have led us. The library of Alexandria was burned deliberately by the Christians in the 3rd or 4th century (the 2nd library, not the one burned accidentally during the BCE war of Julius Caesar with Ptolemy). We didn't have access to Hellenistic copies of Greek and Roman authors until the Muslims brought them to Europe almost a millenium later. Who knows how much time that cost us? We might have self-sustaining solar system colonies and interstellar probes by now, who knows?

The Greeks gave us the first alternative, non-magical, view of reality, a non-anthropocentric natural universe independent of god or man. They invented the concept of nature, and the faith that it was capable of being understood through reason, instead of revelation. Until Europe re-discovered this in the Renaissance, from the old Greek manuscripts, science got nowhere. The Greeks also gave us geometry, mathematical reasoning and Aristotelian logic, number theory and the foundations of analysis; not to mention a head start on almost every modern science. Without that we'd probably be where China was until just a hundred years ago, an advanced civilization with wind and muscle technology but no real science.