In the Roman Republic, the gates of the Temple of Janus, the two-faced Roman God, symbolized wartime and peace. When Rome was at peace, the gates of the temple remained closed. When Rome was at war, the gates would be opened. According to Livy, the Temple of Janus was built by King Numa Pompilius (reigned 715–673 BC). During the 500 year history of the Roman Republic, the gates of the Temple of Janus were closed only twice which means that the Romans were at war almost throughout the Republican age. In the second instance, the gates were closed by Augustus, after the death of Antony and Cleopatra.
The credit for killing the highest number of Roman soldiers in a single day probably belongs to Hannibal. In the Second Punic War, during the Battle of Cannae (2 August 216 BC), Hannibal’s forces trapped a Roman army of 86000 soldiers in a double envelopment tactic and hacked 70,000 Roman soldiers to death in just four to five hours. In the First Punic War, during the Battle of Cape Hermaeum (255 BC), around 100,000 Roman soldiers had been killed due to a sea storm that blew up suddenly and devastated a fleet of 390 Roman warships.
Due to the high casualties that the Roman Republic suffered in wars, which came in quick succession, the Roman society was always plagued by the shortage of men who could serve as soldiers. The birth rate of Roman women was very high during the period of the Republic, and the Romans were able to replenish their population numbers within 10 years of a major war. If the birth rate of the Roman women had been lower, the Roman population might never have recovered. The feminist writer Simone de Beauvoir has criticized the Romans for treating their women as mere soldier producing factories. Simone was probably right. Having enough soldiers to fight the next war was the primary concern for Roman leadership.
The Romans replenished their numbers by granting citizenship rights to the local aristocratic families and in some cases to entire cities. Many conquered cities were given the status of socii, or allies, of Rome. The socii could be moved to a higher level of full citizenship, if they fully cooperated with Rome. The conquered areas were required to pay tribute to Rome but the universal obligation imposed on them was to put their army under Roman control. They had to contribute their young men to serve as soldiers for the Roman army. The Romans were ruthless in dealing with cities which failed to provide tribute and soldiers. They would raze such cities, enslaving their population, and even slaughtering them completely.
As the Romans continued to conquer new cities in Italy, the manpower pool from which they could draw their soldiers became bigger, enabling them to build larger armies with which they subdued the entire Italian peninsula. After that they turned their eyes towards other parts of Europe and towards Sicily and North Africa.