A bronze helmet crest for the "Intercisa II or IV" Roman helmet.  The attaching ends have been lost and there is a hole near the bottom.  The entire piece has the remains of a gold gilding.  The hole does appear to be a wide item, and couple possibly be the tip of some type of bladed item and could easily have occurred during battle as it certainly was facing the primary area of attack on a soldier. 

Here are two other examples, one of which is complete  and the other fragmentary.

The main unique feature on this piece is the symbol that is displayed in this circle (which is surrounded by a dotted border).   

The symbol is called the CHI-RHO.  (*this item also has a star and crescent moon in the field*)

The symbol consists of the superimposed Greek letters chi (Χ) and rho (Ρ) and although commonly connected to Christianity in its earliest form, the symbol also was used prior to Christianity.

What really defines this symbol however is the belief that it was first used by the great Roman Emperor Constantine I (The Great) at the battle of Melvin Bridge on October 28th, 312 AD.  According to one of the sources, Eusebius of Caesarea, Constantine had a vision in which the superimposed letters appeared to him accompanied by the words ‘in this you shall conquer’. A second contemporary source Lactantius, states that Constantine was also instructed to place the symbol on the shields of all his soldiers prior to the battle. History records that this is what he in fact did, and that the result of the ensuing battle was a decisive victory to Constantine and his troops.  Constantine later went on to convert to Christianity on his deathbed, forever changing the course of history as the first Christian Roman Emperor.

Many coins of the period begin to display this symbol on the Military standard and it is consistently displayed on Christian inscriptions.

The item is extremely rare, and it was not until more recently that these items were properly identified.  Previous thoughts had been that they were for belts, or other items.  However the published works of Jelle Prins in 1998 confirmed that these pieces were actually the helmet crest for the Intercisa II or IV Roman helmets.  The portions of a one of these helmets, along with some silver gilt sheathing was located in the Limburg Province of the Netherlands in the later 90's.  The helmet crest still had the bronze attachment on it at the front, with a Chi-Rho emblem engraved on it (very similar to this piece).  (1)(2)(3)

(2)

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Other known examples(1)

Similar Helmet Example with piece superimposed