About 1000 a.c. a Benedictine abbey, dedicated to St. Mary and St. Egidio was founded at Petroio (near Siena) and it seems due to the monks of this estabilishment that something was riade of the agriculture of the valley though there is no documentary evedence that they were actually based here. It does, however, seen very likely that at this period, at the foot of the hills surrounding the valley, where the road that links Cortona with the upper Tiber valley forks towards Perugia a kind of market for the exchange of good was established. This explains the name Mercatale; a market place. The castle at Pierle existed in the 10th century but it is not know when it was built or by when. Like the valley it belonged to the Marquis of Santa Maria del Monte (ancestor of the Marquis of Sorbello owners of the still castle of the same name). This was until the 13th century when Cortona succeeded in taking control and from there on the fate of the valley was closely entwined with that of the nearby city. In the first years of the 14th century the Emperor Arrigo VII thought he had bought peace to Italy, under the control of the German emperor but he was a penniless dreamer, whose only credibility lay in having been crowned by the Pope. In the endless sruggle to find money to pay his German troops and mercenaries who were necessary to hold off his enemies, he offered all kinds of deals and the cortonese thought to profit from this. Thinking they had found someone who would liberate them from the demands of Arezzo. On the 4th September 1321 the emperor greeted the Cortonesi from the steps of the Comune, pocketing a thousand florins that they had managed to find for him. A few months later he died of indigestion at Buonconvento and the Cortonese, along with all the others who had depended on him, were left empty handed. To be sure he had liberated the Cortonese from Arezzo but his premature death made all the decrees he had ordered very uncertain. On top of this they knew that the emperor had tricked them because the day after he left Cortona he gave the Castle of Pierle back to the Marquis of Santa Maria, from whom they had only just succeeded in taking it. A few years later, towards the middle of the 14th century the fate of the Castle was again on the change because Giovanni Visconti tried to impose his rule over central Italy. This decisive and intrepid warrior was close to achieving his aims because he was rich enough to pay for the best mercenaries available. First of all, the armies under his command took Bologna and the romagna and then, through shrewd diplomacy between Pisa, the Casentino the Tiber valley and Perugia he was able to travel south into Val di Pierle which was, and still is, one of the routes between Tuscany and Umbria. Visconti's dreams were brought to an end, however by the florentines who forced his surrender at the battle of Sarzana on the 31st March 1353, just after he had sold the Castle of Pierle to the Oddi family of Perugia. And so 1353 proceeded: France was crippled by the "Hundred years war", Cardinal Albornoz won back, with the sword, the church's possessions in the Romagna, Cola di Rienzo raved in Rome, dreaming of the ancient Republic, the plague spread and millions died of the "black death", Giotto had died a few years before, Orcagna was working in Florence, Dante had been dead thirty years, the fifty year old Petrarch was in Milan and Giovanni Boccaccio was only forty and had yet to write his "Decameron".

If we go back few years to 1325 we find that Cortona was governed by the Casali family with the title of "Vicar Imperial" even if they exercised the powers confered on them mainly for their own benefit. It was Bartolomeo Casali who defined the boundaries between Cortona, Perugia, Citta di castello and the val di Pierle, where the family had had lands and houses for at least fifty years. At this period Perugia had control over not only Pierle but also over Mercatale and the fortress of Danciano, but eventually the Casali managed to regain what they considered to be cortonese territory. This made little or no difference to the people who lived in the valley because this went badly who ever was in control; they still had to work for, and pay taxes to, their masters who were equally grasping and mean. Life become so unsupportable for these pour people that on the 11th August 1369 they did the unthinkable. The farmers of Pierle armed with hoes, forks and sticks attacked the home of the Casali in Mercatale, broke down the door and sacked the store rooms. The Commander of the garrison of Pierle mobilised his troops to put down the insurrection and three people were killed. Perhaps because of this trouble the Oddi counts from Perugia preferring to distance themselves from such a troublesome area sold Piere and the Castle at Lisciano to the Casali. Now they had control over the valley they undertook the reconstruction of the castle at Pierle by now in a poor state of repair. It was a family affair: the project for the new castle was in the hands of one of Casali's son, Ranieri who had some experience of military architeture, having been a knight of Rodi. The remains of the old building were knocked down and the new fortress was built within a curtain wall perched on the vantage point with walls substantial enough to accomodate sentinels, a walkway for guards and arrowslits and made all the more defensible with four towers. The entrance was protected by a drawbridge. It because a real fortress, strong enough to resist a full pitched attack. The building stone was mestone from a marry on site and no expense was spared because a ready supply of workmen was available locally. The castle served to protect the people of the valley and as a refuge for them when they were attacked by some band of brigands.When in 1383 the plague took hold again in Cortona the Vicar Imperial Niccolò Casali crossed the mountain and sought refuge in Pierle. For other members of the family the castle took an a more sinister nature; suspected of cospiring some were imprisoned in the castle where they were tortured, according to the cruel customs of the times. In the early 1400 the bloody era of the Casali cameto its end thanks to help of Ladislao D'Angiò Durazzo king of Naples, who wanted to become king of Italy by annexing most of the country. He had already laid hands on Rome, Milan, on the Romagna and Marche and was preparing to manch on Florence and Siena. Held up by resistance of these two city he turned his attention to Arezzo and encamped at Ossaia. It was 1409. Even though his troops did not reveal themselves to be particularity good allies (in one day they burned the crops in the Val di Chiana and burnt down the houses in Camucia, Montalla and other Cortonese's villages) the Cortonese hoped that the king wold liberate them from the Casali and to show hon determinated they were they rebelled and delivered the city to king Ladislao. Freedom was shortlived because Ladoslao was forced to sign a treaty with Florence and Siena. The Fiorentines paid 600 thousand florins and bought Cortona which stayed in their hands from there on. They also paid 1200 florins for the Castle of Pierle. They garissoned it with four armed guards, crossbownen and troops a castellan and determined to mantain public order in the valley. A valley which marked the borders (and still does) between Tuscany and Umbria. From this point onwards the castle loses all its strategic weight and any time an armed band wanted to cross the Val di Pierle it did so. As, for example, in 1501 when Vitellozzo Vitelli, lord of Citta di Castello, took control of Mercatale for ten years and in 1510 when the army of Malatesta Baglioni passed through on its way to Florence. Soon the Castle become a refuge for bandits, brigands and outlaws, political refugees and all sorts of people who prefer to travel by unfrequented roads. In 1576 Francesco dei Medici, GranDuke of Tuscany, decided to put an end to the problem and ordered that the old castle be made uninhabitable. Its anches and walkways were destroyed with the roof, reducing it to the ruins we see today.