If it does not join two cables, then it is a housing for a pulley so a cable can make a right angle turn.
You did not say it joined 2 cables, you said it was a splitter. It does join 2 cables. It is a watertight cast-iron junction box that was used to join two sets of wires underground. Nice job Red!
I meant splitter as in joining two cables into a single cable, assuming that there was a third cable out of view.