Inside the main altar, in the Teodolinda’s Chapel, which is held the Iron Crown, one of the most important goldsmithery’s masterpieces in the whole Western history. Conserved as a miracle until now, the Crown is composed of six golden plates – adorned with rose relieves, gems settings and enamel – with a metal ring inside, that names as “iron” the Crown, told by tradition by Saint Ambrose at the end of the IV century, knowing the ring itself is said to be a nail from the crucifixion of Jesus Christ. A holy relic that Saint Helen found in 326, moving to Palestine and then put into her son’s crown Constantine the Emperor.
The tradition that ties up the Crown to the Passion of Christ and to the first Christian emperor, tells the symbolic value given by the kings of Italy (and by those who would have been so called, like the Viscontis) and all them who would have used it to coronate with the divine origin of their own power, strictly tied up with the Roman emperors of the past. Recent tests done to the Crown let us suppose that – as it looks today – it was customised in between the IV-V and IX centuries and it could have been also a late insignia of Royalty, since the Longobard kings to the Carolingians, those who restored and gave it to the Duomo of Monza.
Since that moment the history of the Coronet became strictly close to Monza and its Duomo. For instance, in 1354 Pope Innocent the IV sanctioned as a right – lately resolved anyway – that the Duomo of Monza could host the Italian kings coronations, then Saint Charles Borromeo in 1576 established the Holy Na l’s Cult, right to formalise the identification of the Coronet as a relic and also to tie the Crown to another Holy Nail, conserved in the Duomo of Milan, that for the same ancient tradition Saint Helen would have mould and shaped onto Constantine’s horse’s bite, considered a metaphor of the divine inspiration to lead the empire.
Due to its sacred value the Iron Crown is held inside a dedicated consecrated altar, built by Luca Beltrami in 1895-96.