https://www.jewishvirtuallibrary.org/the-amidah>The Amidah is the central prayer of all four services: shacharit (morning), mincha (afternoon), maariv (evening), and mussaf (additional). The word Amidah literally means standing, because it is recited while standing. It is also known as Shemoneh Esrei, meaning eighteen, because it originally consisted of eighteen blessings, and as tefilah (prayer) because it is the most important Jewish prayer. The obligation to pray three times a day, which was established by Ezra and codified in the Talmud (Berakhot 26b), is fulfilled by reciting the Amidah. >The additional blessing (against heretics) was initially meant to combat the threats posed by the Samaritan and Sadducee sects, and was permanently added to the liturgy when Jewish converts to Christianity began to inform on Jews to the Roman authorities. https://www.tzion.org/articles/EighteenBenedictions.htm12. Prayer against slanderers (added later at Yavneh)
And for slanderers let there be no hope, and let all wickedness perish as in a moment; let all Your enemies be speedily cut off, and the dominion of arrogance uproot and crush, cast down and humble speedily in our days. Blessed art thou, O L-rd, who breaks the enemies and humbles the arrogant.
This addition to the Shemoneh Ezreh brings the count of blessings to 19 instead of the 18, as indicated by its name. The prayer against slanderers was added at Yavneh placing it during the time of the beyt midrash at Babylon, (See Barachoth 33a) This prayer was aimed at "Christians" according to Rabbi Jeffery Cohen, author of Blessed Are You.
