Table schema:
CREATE TABLE table_name_51 (place_of_birth VARCHAR, elevator VARCHAR, elector VARCHAR)

Question: What's the Place of birth listed that has an Elevator of ALexander III, and an Elector of Ruggiero Di San Severino?
SQL: SELECT place_of_birth FROM table_name_51 WHERE elevator = "alexander iii" AND elector = "ruggiero di san severino"