In Easter 367 AD, Athanasius of Alexandria issued his 39th Festal Letter — the annual letter announcing the date of Easter to the Egyptian churches. Embedded in it is the first surviving list of the 27 New Testament books we use today, exactly as we have them now, with the explicit instruction that "in these alone is the teaching of godliness proclaimed."
Why this matters
The first complete, named list of the 27-book New Testament canon. Settles questions about which books the early church considered scripture. The letter reflects a consensus that had been forming for centuries; it didn't create the canon, it ratified it.
Scripture references
MatthewJohnRomans1 JohnRevelation
Location
Alexandria