In the spring of 568 King Alboino, on the shores of Lake Balaton gathered the Lombard people and began his advance in Italy, at the head of armed men, women and children. Despite the scarce consistency of the invaders, the Byzantines were unable to effectively counteract their advances and, avoiding major battles, they concentrated on the defence of castles and fortified cities.Thus in Po Valley, the Lombards conquered Vicenza, Verona and Milan and besieged Pavia for three years; meanwhile Alboino went down towards Tuscany, occupying Lucca around 572, which became the seat of a new duchy.
In the Apennines the defence of the fixed fortifications' network by the Byzantines allowed the growth of defense's lines generally indicated with the name of 'limites'' that in some areas stopped for a long time the invaders. From Lucca they descended towards north Tuscia and then down to Spoleto and Benevento. In Valdinievole the Lombards were blocked in their advance towards Pistoia for 20 years along the Byzantine limites which had its strongholds in the fortifications of Serravalle (La Maggiore), Castelvecchio and Verrucca.
Here, the Lombards placed armed escorts on the top of the hill that faces the pass and that still today is called 'of the Guardia', from the Lombard lemma ward, which means precisely armed sentry. On the first hills that delimited the flat belt of the Valdinievole, arimannic groups were established, i.e. armed familie coterie to which the King granted the use of land assets as economic compensation of 'their stable military and localized service'.
In Montecatini Terme and Buggiano, it is possible to identify these arimannias, places where still in the twelfth century there were factions of 'Lambardi', heirs, if not descendants, of the ancient Arimanni.
Meanwhile, the Lombard advance continued southwards along the Cerbaie hills, located between Lake Sesto (today Padule di Bientina) and the Padule di Fucecchio, along a route that later became the important 'Via Francigena'. (from 'The Byzantine Limes in Valdinievole' by N. Rauty, 1989, Proceedings of the Conference I Castles in Valdinievole-Buggiano Castello).
Poggio alla Guardia constitutes one of the last reliefs before reaching the alluvial plain formed from the sediments of the Torrente Nievole (Nievole torrent) that flows into the depression of the Fucecchio Marshes.
It's entirely formed by a geological formation called 'Formazione di Monte Morello' (Monte Morello's formation), in the province of Prato, consisting of white marble limestones and subordinately calcarenites with dark gray fissile shales deposited in the period between the Upper Cretaceous and the Lower Miocene (approximately 70-60 million years ago), belonging to the Unity of Alberese, a tectonic unit of Ligurian origin.
The main tree species is Roverella (Quercus pubescens), a very common oak in the Tuscan hills, together with Orniello threes (Fraxinus ornus), rural Elm (Ulmus minor) and many other shrub and herbaceous species; mostly along the sunniest slopes of the hill, there are numerous species, which are part of the Mediterranean vegetation as Fillirea comune ((Philiyrea latifolia) and Alaterno (Rhamnus alaternus), Myrtle (Myrtus communis) and Spanish broom (Spartium juncaum), female Cistus (Cistus salvifolius), Viburnum (Viburnum tinus), Pugent asparagus (Asparagus acutifolius) and the thorny lianas of the Stracciabrache (Smilax aspera).
Other characteristic aspects of the landscape are olive groves, which form a wide arc along the hilly slopes of the Poggio della Guardia.
Between the wood formations and the cultivated areas, the dominance of shrub and lianose species that colonize degraded wooded areas and old quarry areas is very frequent; among the most characteristic species there are Brambles, the creepers Rubia Peregrina and Similax aspera, Hawthorn (Crataegus monogyna), Female cistus, Spanish broom, Sanguinello (Comus sanguinea), Heather (Erica arborea) and Pungent asparagus.
Modest surfaces are characterized by the presence of tree formations dominated by Robinia
(Robinia pseudoacacia), an American invasive species; the undergrowth, floristically poor, is mainly composed of Brambles and Black Elder (Sambucus nigra). Numerous spontaneous Orchids.
The marly limestones of Monte Morello, which emerge at Poggio alla Guardia, have been interested up to 30's of the twentieth century from quarrying activities, aimed at the extraction of marl from cement by the Minnetti company called 'la cementizia' (the cementitious).
The quarry was partially cultivated outside, but also had an intense mining activity in tunnel.
This cultivation developed on three distinct levels where the lowest had the function of collector for the materials extracted from the upper floors, connected to the base level by some descenders. The material was extracted with explosives, picks and chisels; it was ground and then transferred by a cableway which crossed the whole area at the foot of the hill up to the current Provincial road, where there were the working factories. Even today in Poggio alla Guardia it is possible to find squares and quarry roads, as well as infrastructures created for the storage and transport of materials.
Today, the Portland Cement is totally obtained in the right proportions, pure limestone (78%) and clay (22%), since the outcrops of marly limestone which naturally present the right concentration of the two minerals would not be enough to provide the raw material to produce all of the cement required by the market.