Tatian

[W]e have almost the entire corpus of the Gospels in the Diatesarron, and in them, from at the latest 180AD, we see statements of Christ's divinity. And he was a heretic who wrote it, but they're all quotations from the Gospels, directly. We can safely assume the Gospels are 100% perfect. He was trying to unify them, when we need them in those four separate sources, to account their witness, but it's all there, and early. And we know from that, the Gospels are highly established, as they're being referenced to, to compile the document. And Mark is the least quoted of all four.