Where does “класться” come from?

класться (Russian) comes from Russian -ся, from Old East Slavic сѧ, from Proto-Slavic sę, from Proto-Balto-Slavic *sen, from Proto-Indo-European swé — self.

Ancestry of “класться”, step by step

StepLanguageWordMeaning
1Russian-сяReflexive suffix appended to finite verbs and...
2Old East Slavicсѧ—
3Proto-Slavicsęoneself: myself, yourself, himself, herself,...
4Proto-Balto-Slavic*senoneself
5Proto-Indo-Europeanswéself
Every word from Proto-Indo-European swé →Every word from Russian -ся →Every word from Proto-Balto-Slavic *sen →