The Treaty of Ste.
A group of farmers in India did this after seeing water dropletsfloat in the air. The Treaty of Ste. Claire-sur-Epte mandated that one of its signatories do this, and Duke Mojmir of (*)  Moravia did this only to have his brother take an opposing course. At the urging of Frumentius, King Ezana of Axum did this, and a Sioux chief's son who did this took the name of Charles Eastman and co-founded the YMCA. Refusing to do this action in reverse caused the execution of King Ella of Northumbria by Vikings. For ten points, name this action that usually involves baptism in a local river.
A group of farmers in India did this after seeing water dropletsfloat in the air.
Converting to Christianity