The bottom line is that when we have large numbers of historical documents or fragments on a particular topic dating from or faithfully transcribed from ancient times, then we can consider the history gleaned from them remarkably accurate.
For instance, no one—especially your literature teacher—questions the authenticity of the epic poem The Iliad by the ancient Greek poet Homer. In fact, it is the second most well-documented historical writing in existence, with 643 manuscripts still surviving, the oldest complete text dating from the 13th century. Quite impressive!
Now consider the ancient text that is the most well-documented.
By a late 20th-century reckoning, there are over 5,300 surviving ancient Greek manuscripts, 10,000 in Latin and over 9,300 other early-language versions for a grand total of 24,633 manuscripts of this document—the one we call the New Testament of the Bible! This amounts to phenomenal historical validity. This ancient text, by far the most reliably preserved of any, thus validates Jesus Christ's historical existence (Josh McDowell, Evidence That Demands a Verdict, Vol. 1, pp. 39-40).