This family has very ancient origins. As the Malavolti states, it is plausible that the Piccolomini are of Frankish or Germanic origin, like many other ancient Sienese families of the time, as it would seem to emerge from a 1098 purchase deed, where a Martin of Piccolomo declared to live together to his wife Rozza under the Longobard law.
Around the middle of the fifteenth century writings about the mythical origin of the family began to flourish. The Florentine poet, Leonardo Dati, at the court of Pope Pius II, translated, from the Latin, a libretto by Caio Vibenna, in which appeared a Bacchus of Piccolomo, lord of the castle of Montone, called by the king Porsenna to rescue, Tarquinio the Superbo chased away from Rome.
Pope Piccolomini, far from being tempted by these mythical suggestions, was convinced, however, that his family was rooted in ancient Rome, due to the frequent use of the names Silvio, Enea or Ascanio.
In the seventeenth century two Piccolomini brothers from the Modanella branch were about to make a large family tree. To seal, with a legal certification, their ancient genealogy, they entrusted a notary, Alessandro Rocchigiani, to put order in the various sources that disserted on the origin of the family. Evidently the charm of the myth, mixed with reverence due to the illustrious clients, instead of eliminating the legendary components ended up increasing them. Orazio Coclite, was indicated with certainty by the zealous notary, as the new progenitor of the family. Undoubtedly some coincidences are awe. In fact, in the column that adorned the Campidoglio, his undertaking, identical to that of the Sienese family, stood out in the shield of the ancient Roman.
Once attached to Horace, the lineage of the Piccolomini family had, in ancient Rome, the name of Parenzi and from there, then a component of it, chose as a new residence the Sienese colony. Where he abandoned his name, Chiaramontese, to change it into Piccholuomo.
In more recent times, the oldest reference to the Piccolomini, emerges when Siena was not yet erected to the Republic. The emperor Arrigo II, named Salamone Piccolomini, his procurator and governor of the Sienese territory, in 1055 and according to what asserts the Bisdomini, he and his brother Matteo built two city towers, one of which on the road leading to Rome.
At that time their coat of arms was not yet well defined, and often in the blue cross appeared more half-moons than the five commonly known.
They are remembered as belonging to the Great of Siena and were among the first to be ascribed to the mountain of the Gentiluomini. Rustichino of Orlando and Guglielmo di Piccholuomo participated in the city government as "Consuls" of the young Republic in 1160 and 1170. Rainerio di Montonio and Rustichino di Piccolomo in 1178 and 1228.
Already from very remote times they owned the castle of Val di Montone which stood on one of the three hills close to which the urban fabric of medieval Siena would have developed. In 1220, Engelberto or Inghilberto d'Ugo Piccolomini received the fief of Montertari in Val d'Orcia by Emperor Federico II as a reward for services rendered.
The family acquired palaces and towers in Siena and various castles in the territory of the Republic. Some of the oldest of these properties, such as Montone and Castiglione, were sold in Siena in 1321.
The Piccolomini obtained great wealth through trade and established accounting offices in Genoa, Venice, Aquileia, Trieste and in various cities of France, England, Germany and Austria.
Supporters of the Guelph cause, when the Ghibelline party, in 1260 with the Battle of Montaperti triumphed in Tuscany, were forced, like so many others, to take the path of exile and their houses and possessions were devastated and destroyed. They returned home with French help, but were again expelled during the short reign of Corradino di Svevia. After the battles of Tagliacozzo (1268) and Colle val'Elsa (1269), in which the Swabians and the Ghibellines were finally defeated by Charles I of Anjou, the Piccolomini returned triumphantly to Siena and persecuted with determination the members of the Ghibelline faction .
These continuous struggles between different factions, significantly weakened, the commercial influence of the Republic, to the full advantage of Florentine rivals, who were strong in the Guelph victory and occupied the most important trade nodes, previously held by the Sienese. In this context, the Piccolomini, more forward-looking than others, withdrew from the trade, avoiding the long chain of failures that involved other powerful Sienese families.
While continuing to dedicate themselves to the consolidation of their wealth and their land domination, albeit with discretion and discretion, they remained at the top of the state and actively participated in the government of the republic, being their prestige remained unaltered.
Through the various branches of the extended family, over the following years, their lordships in Alma, Castiglioncello, Amorosa, Roccalbegna, Torre a Castello, Porrona, Triana, Castiglione d'Orcia, Ripa d'Orcia, Batignano, Celle, Castiglione della Pescaia, Radicofani, the aforementioned Montertari, Sticciano, Modanella, Montemarciano, Camporsevoli, Isola del Giglio, Castiglion del Bosco, Capestrano, Celano, Amalfi, Nacod in Bohemia, Valley in the Kingdom of Naples.
They also owned Corsignano, later called Pienza, the fortress of Castiglion Baroti, Bibbiano Cacciaconti and Bibbiano Guilleschi, Castelnuovo Berzi and vast territories in Montalcino, Rosia, Radi, Arbiola, Asciano, Abbadia Ardenga, Montefollonico, Rapolano, Poggio S. Cecilia, Montichiello, Bettolle, Vergelle and other minor places.