In 1204, the transfer of the bishopric from Luni to Sarzana,marks the end of the Roman city , now reduced to a heap of ruins from the succession of barbarian invasions and from the gradual silting of the harbor.
From this moment Sarzana definitively replaces Luni in the dominion of an extensive and disputed territory ,that will definitively pass under the rule of the powerful Maritime Republic of Genoa.
The town, located along the Via Francigena and the Via Aurelia, increases more and more in importance and becomes a key passage for pilgrims, merchants and knights traveling to Rome.
In this context it begins the construction of the cathedral of Santa Maria Assunta, in which were transferred from Luni the relic of the Precious Blood and the Crucifix by Master William (1138), considered the prototype of the crosses painted all over Tuscany.
In the Renaissance period Sarzana reach the peak of its development, as witnessed also by the construction of massive fortifications such as the Medici Citadel and, above all, the Sarzanello fortress , a splendid example of military architecture of transition between the Middle Ages and the Renaissance, built according to the dictates of Francesco di Giorgio Martini.