1,700. Witnesses to the Get

Hilchos Geirushin 1:13

We see that a get must be given in front of witnesses from Deuteronomy 19:16, “The matter will be established based on the word of two witnesses or three witnesses.” It’s inconceivable that one day a woman should be prohibited and intimate relations with her punishable by death, and the next day she should be permitted, unless there are witnesses to this change in status. Accordingly, if a man gives a get in private, or even in the presence of just one witness, divorce is not effected.

Hilchos Geirushin 1:14

The above halacha applies when the get was written by a scribe. If the husband wrote the get himself and only one witness signed it, after which the husband gave it to his wife, then divorce is effected at the Torah level and voided by rabbinic enactment (putting the woman in a quasi-divorced position).