Read this: During this period, Roman soldiers seem to have been modelled after those of the Etruscans to the north, who themselves seem to have copied their style of warfare from the Greeks. Traditionally, the introduction of the phalanx formation into the Roman army is ascribed to the city's penultimate king, Servius Tullius (ruled 578 to 534 BC). According to Livy and Dionysius of Halicarnassus, the front rank was composed of the wealthiest citizens, who were able to purchase the best equipment. Each subsequent rank consisted of those with less wealth and poorer equipment than the one before it.
Now answer this question, if there is an answer (If it cannot be answered, return "unanswerable"): Who introduced the phalanx formation into Rome's army?
Servius Tullius