No text in Proto-Germanic survives, because the language had already begun splitting into its daughter branches, East, North and West Germanic, by the time any Germanic people wrote anything down. Everything known about it is reconstructed by the comparative method, working backward from Gothic, the earliest well attested Germanic language, recorded in Bishop Wulfila's fourth century Gothic translation of the Bible, together with Old Norse, Old English, Old High German and Old Saxon, comparing shared and divergent sound patterns and vocabulary to infer the common ancestor form beneath all of them, and cross-checking the result against Proto-Indo-European, from which Proto-Germanic itself is judged to descend. This method identified Grimm's Law, the systematic consonant shift, first Indo-European voiceless stops becoming Germanic voiceless fricatives among other changes, that separates Germanic from its Indo-European relatives and gives words such as English father and Latin pater their related but shifted initial consonants.
Linguists date Proto-Germanic's unified existence to roughly the middle of the first millennium BC, based on the degree of divergence already visible among its earliest daughter languages, though because it was never written the dating rests entirely on internal linguistic evidence rather than any external record, and reconstructed forms are conventionally marked with an asterisk to signal that they are inferred rather than directly attested.