Where does “puerta” come from?

puerta (Old Spanish) comes from Latin porta, from Proto-Indo-European per-, from Proto-Indo-European pr̥tós — passed , crossed.

Ancestry of “puerta”, step by step

Step	Language	Word	Meaning
1	Latin	porta	gate, especially of a city; entrance, passage,...
2	Proto-Indo-European	per-	before, in front; first; to go through
3	Proto-Indo-European	pr̥tós	passed , crossed

puerta — Etymology, Origin & Word History | Etymology Explorer