Known as the first castle in the whole of the Lucchesia, Santa Maria a Monte was an outpost of the Bishops of Lucca who aimed to strengthen the southeastern borders of the Diocese, by profiting of its strategic collocation, as it was wedged between the rivers Arno and Arme (the current Chiamiana), with the hill enjoying a privileged position on the Lower Valdarno, close to the dominions of Florence and Pisa.
Already attested from 906 AD, the first castellum was in all likelihood characterized by a tonimen, that is a defensive and fortified wooden palisade that protected the highest section, where there stood a Longobard oratory with a single rectangular hall measuring 23 x 11 m, as well as various dwellings in perishable material such as wood or raw earth.
In the mid-thirteenth century, when the commune of Lucca took possession of the castle, subjected it to extensive fortification works, and equipped it with three defensive wall systems. The second of these hinged to the domain of Castelvecchio, dominated by a dungeon to protect the area, while the third, the outermost one, was to defend the entire castle. The highest sector – that of the Rocca, that was equally armed – was characterized by the presence of a palace, seat of the Bishop of Lucca, and a fortified church, the result of the expansion of the ancient Longobard oratory.
This parish church was dedicated to Maria Assunta. It was characterized by two opposing apses and a longitudinal body structure formed by the original religious nucleus of the ancient oratory. To the east, the parish church presented a large three-apsed cross-shaped transept on two levels, added in the mid-eleventh century. It was the Bishop of Lucca Giovanni II who established a regular rectory, made up of 14 ecclesiastics, including priests, deacons and clerics, and who also endowed the place with a n episcopal palatium.
The lower level of the transept corresponded to an oratory crypt, divided by cross vaults supported by eight columns; access was guaranteed by two narrow ramps. Its apses still retain the traces of the three original altars. The Pieve had its own baptismal font, which in the thirteenth century was to replace the extant 10th-century octagonal font. Enclosed and defended by a high escarpment bastion that stood in lieu of the old wooden defenses, the religious building was a real parish church, made by regularly hewn stone ashlars, a hut roof, the entrance carved in a portal presumably located on the north side, by virtue of the baptismal font which occupied the entire west area of the church, where there was a tribune dedicated to San Genesio.
The current spiral urban layout still quite faithfully respects the original architectural plan of the castle as it likely was in the Middle Ages. The village was accessed through three gates surmounted by towers equipped with trapdoors, while the defenses were dotted strategically with other towers. Today still stand traces of this formidable defensive system, as it was defined by the historian Villani on the occasion of the Florentine conquest of 1327: some of these towers were refurbished during the first half of the eighteenth century – such as the Tower of Castruccio Castracani – to protect the second ring of walls, the north east corner turret and the south west corner turret, both on the outermost wall circle; others remain still almost intact, such as the current bell tower of the Collegiate Church, an ancient watchtower, or the Clock Tower, originally placed to defend the intermediate walls and later equipped with working bells. The bastion of the Rocca is also well preserved, with a polygonal plan supported by a high shoe made entirely of brick, arranged on each side in the outer wall curtain enclosing the hillside.
Other traces are lost, such as Porta al Mercato, which takes its name after the weekly market that took place in the nearby square, later occupied by the bulk of the eighteenth-century Palazzo Scaramucci; Porta San Giovanni, preceded by an anti-door, placed next to what would later become the future Collegiate Church rededicated in 1466; and like all the defensive system located upstream of the castle: in fact in 1850, to allow easier access and exit for the inhabitants it was created Via Nuova (today Via 2 Giugno), for which the walls were dismantled that connected the bastion of the Rocca to the ancient Porta Guelfa, whose powerful quadrangular foundations emerged, approximately at the same time as the renovation of Piazza della Vittoria.
Placed to guard one of the three entrances to the castle, probably of Castruccian foundation (first quarter of the fourteenth century), the north-west access was strengthened in 1327, once the Florentines got hold of the castle.
If the archaeological excavations completed in 2013 outline the patterns of the highest part of the castle as it likely was in 1327, it is more difficult to reconstruct the foyer that the Florentines, once they had conquered the castle, decided to build, in lieu of the religious building.
The only structure belonging to the ancient fortress appears to be a quadrangular cistern which, a few meters underneath (as can be deduced also from the presence of the adjoining water adduction/ capture well), was built for the storage of drinking water, an indispensable element for the military garrison which had to be able to withstand even prolonged sieges by enemies. This cistern probably served the foyer which, connected to the Rocca tower, allowed the Florentine guard to defend the last military garrison of the castle.
By analogy, it would not be out of place to assume that the fortress was similar to that of the Castello dei Vicari at Lari, or to the foyer of Ripafratta. With its reduced proportions, the fortification, supported by a high brick shoe, had an orthogonal curtain within which the buildings of military relevance were dominated by a high and mighty tower, the re-adapted bell tower of the old Pieve, as displayed in many later perspective views of the castle.