Conversely, I always hear the claim that Jesus was born on 1 AD, but on what evidence do we know that? Some random monks in the dark ages tried to guess so they

Conversely, I always hear the claim that Jesus was born on 1 AD, but on what evidence do we know that? Some random monks in the dark ages tried to guess so they could make a calendar, and that's the guess they came up with. While the modern estimate certainly has uncertainty too (how could we ever _know_ such a thing with complete certainty?), there's no way it's _less_ accurate than the original estimate made by some random monk in the middle ages, working with much less data. It does not make sense to privilege that random monk's guesses over today's guesses. According to Wikipedia, there's two different methods -- written Roman records of Herod as mcphage mentions, or using written Roman records of Pilate's crucifixion and subtracting the claimed age of Jesus at that time. Both methods give years that are in the same ballpark, roughly 4 to 6 BC, which should give confidence that they are close. No method gives an answer of around 1 AD. (Actually, it's pretty impressive that some monks working hundreds of years later in the dark ages are no more than a few years off from today's best estimates)