The Iron Crown is so called from a narrow band of iron within it, said to be beaten out of one of the nails used at the Crucifixion. This very thin band is about three-eighths of an inch broad. According to tradition, the nail was first given to Emperor Constantine by his mother Helena, who discovered the Cross. How it fell into the hands of the Lombard kings is not well esplained. The outer circlet of the crown is of six gold and enamel segments of beaten gold, joined together by hinges and set with precious stones that stand out in relief, in the form of crosses and flowers.
Its small size and hinged construction have suggested to some that it was originally an armlet or perhaps a votive crown that was presented to the Cathedral of Monza, where it is preserved as a holy relic. On 23 March, 1026, Heribert, the archbishop of Milan, crowned Conrad II at Milan with the iron crown of Lombardy. From the 9th to the 12th cent. the Italian kings, and several German kings, received the Iron Crown of Lombardy at Pavia.
On the 23rd of May, 1805, Napoleon had himself crowned King of Italy at Milan, with suitable splendor and magnificence. Seated upon a superb throne, he was invested with the usual insignia of royalty by the Cardinal Archbishop of Milan, and ascending the altar, he took the iron crown, and placing it on his head, exclaimed, being part of the ceremony used at the enthronement of the Lombard kings, Dieu me la donne, gare à qui la touche-- 'God gives it me, beware those who touch it'.
On the occasion, Napoleon founded the Order of the Iron Crown, on June 15, 1805. After Napoleon's fall and the annexation of Lombardy to Austria, the order was re-instituted by the Austrian Emperor Francis I, on January 1st, 1816. Emperor Ferdinand I decided to have himself crowned King of Lombardy and Venetia in Milan on September 6, 1838, using the Iron Crown. After the war between Austria and Italy, when the Austrian had to withdraw from Italy in 1859, the Iron Crown was delivered to Victor Emmanuel.
A surprising image of the Iron Crown figures in Chaper 37 'Sunset' ofHerman Melville's Moby Dick. The brief chapter is devoted to Captain Ahab's soliloquy. Among his delusions of persecution and of grandeur, he imagines himself crowned with the Iron Crown of Lombardy, an unexpectedly erudite touch for Ahab, though perhaps not for Melville.
Reference
E. Cobham Brewer, Dictionary of Phrase and Fable, 1898.