According to Titus Livius there were seven kings of Rome from 625 - 510 BCE. From top to bottom they were;
Romulus (R. 753-715 BCE),
Numa Pompilius (R. 715-673 BCE),
Tullus Hostilius (R. 673-642 BCE),
Ancus Marcius (R. 642-616 BCE),
Tarquinius Priscus (R. 616-579 BCE),
Servius Tullius (R. 578-535 BCE) and
Tarquinius Superbus (R. 535-510 BCE).