Nails with which Our Saviour was fastened to the Cross, and which according to tradition were found by Saint Helena. It is not certain whether there were three or four, more probably four. Saint Ambrose and others record that Saint Helena had one nail converted into a crown for Constantine and another one into a bridle for his horse. It is probable that the iron crown of Lombardy, preserved at Monza, Italy is identical with this crown. The holy nails venerated in more than 30 places of Europe are imitations, some of which may contain filings of the true nails.