In heraldry nine crowns are recognised: The oriental, the triumphal or imperial, the diadem, the obsidional crown, the civic, the crown vallery, the mural crown, the naval, and the crown celestial.
The blockade crown (corona obsidionalis), presented by the Romans to the general who liberated a beleaguered army. This was made of grass and wild flowers gathered from the spot.
A camp crown was given by the Romans to him who first forced his way into the enemy's camp. It was made of gold, and decorated with palisades.
A civic crown was presented to him who preserved the life of a civis or Roman citizen in battle. This crown was made of oak leaves, and bore the inscription, H.O.C.S. —i.e. hostem occidit, civem servavit (a foe he slew, a citizen saved).
A mural crown was given by the Romans to that man who first scaled the wall of a besieged town. It was made of gold and decorated with battlements.
A naval crown was by the Romans given to him who won a naval victory. It was made of gold, and decorated with the beaks of ships.
An olive crown was by the Romans given to those who distinguished themselves in battle in some way not specially mentioned in other clauses.
An ovation crown (corona ovalis ) was by the Romans given to the general who vanquished pirates or any despised enemy. It was made of myrtle.
A triumphal crown was by the Romans given to the general who obtained a triumph. It was made of laurel or bay leaves. Sometimes a massive gold crown was given to a victorious general. (See Laurel.)
The iron crown of Lombardy is the crown of the ancient Longobardic kings. It is now at Monza, in Italy.
Henry of Luxembourg and succeeding kings were crowned with it. Napoleon I. put it on his head with his own hands. It is a thin fillet of iron, said to be hammered from a nail of the true cross, covered with a gold circle, enamelled with jewels, etc.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894