Siena, like other Tuscan hill towns, was first settled in the time of the Etruscans (c. 900–400 BC) when it was inhabited by a tribe called the Saina.
The Etruscans were an advanced people who changed the face of central Italy through their use of irrigation to reclaim previously unfarmable land, and their custom of building their settlements in well-defended hill-forts.
A Roman town called Saena Julia was founded at the site in the time of the Emperor Augustus. The first document mentioning it dates from AD 70. Some archaeologists assert that Siena was controlled for a period by a Gaulish tribe called the Saenones.
The Roman origin accounts for the town's emblem: a she-wolf suckling infants Romulus and Remus. According to legend, Siena was founded by Senius, son of Remus, who was in turn the brother of Romulus, after whom Rome was named.
Statues and other artwork depicting a she-wolf suckling the young twins Romulus and Remus can be seen all over the city of Siena. Other etymologies derive the name from the Etruscan family name "Saina," the Roman family name of the "Saenii," or the Latin word "senex" ("old") or the derived form "seneo", "to be old".
Siena did not prosper under Roman rule. It was not sited near any major roads and lacked opportunities for trade.
Its insular status meant that Christianity did not penetrate until the 4th century AD, and it was not until the Lombards invaded Siena and the surrounding territory that it knew prosperity.
After the Lombard occupation, the old Roman roads of Via Aurelia and the Via Cassia passed through areas exposed to Byzantine raids, so the Lombards rerouted much of their trade between the Lombards' northern possessions and Rome along a more secure road through Siena.
Siena prospered as a trading post, and the constant streams of pilgrims passing to and from Rome provided a valuable source of income in the centuries to come.
The oldest aristocratic families in Siena date their line to the Lombards' surrender in 774 to Charlemagne. At this point, the city was inundated with a swarm of Frankish overseers who married into the existing Sienese nobility and left a legacy that can be seen in the abbeys they founded throughout Sienese territory.