"The Diatessaron" was composed by Tatian, a second-century writer and theologian, around 160-175 AD. Tatian compiled The Diatessaron to provide a unified account of Jesus' life, teachings, death, and resurrection, using the existing papyri in circulation. These papyri were compiled into what became known as a "codex", an early version of a book!

You might call The Diatessaron the very first Bible. Long before the council of Nicea, this incredible compilation existed.