How do we know when the Gospels were written?

Most scholars--probably even fundamentalists--agree that the Gospels were written several decades after the time they purport to cover. But what is the basis for these beliefs? Is it the apparent errors, contradictions, and other inconsistencies; or is it the language the Gospel writers used, frequently alluding to events that happened much later? Is it universally accepted that the Gospels were written near the end of the first century A.D. (or even later), probably after the Pauline and other Epistles were written?(I suppose this should go into the Accuracy/Inerrancy forum, unless there's a better fit somewhere else.)

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