There is a locative case in Proto-Indo-European, but in many later languages it merged into other cases, Slavonic languages being an exception. (So Slavonic didn't invent the locative case.)
Old Latin had a functioning locative case, but for a number of reasons (like shift in pronunciation), the locative case merged for the most part into the ablative in Classical Latin.
So, in Classical Latin the locative is only fully functioning for small islands and towns or cities (e.g. Roma → Romae, Athenae → Athenis). In addition, there are a few fossilised instances of the locative case, like domī, rūrī, humī. You probably learn these as exceptions in a basic (Classical) Latin textbook.
visam, si domi est
I will see, if he is home
from Heauton Timorumenos