Today the Catholic Church celebrates the Feast of St. Januarius (San Gennaro), bishop and martyr. San Gennaro is the patron of Naples, which possesses several major relics. Of these, the most famous is a vial of the saint's blood, which on several days throughout the year (his feast, the feast of the translation of his relics, etc.) miraculously liquefies.
I have SEEN this miracle.
The glass vessel is carried through the streets of Naples in procession, preceded by the parishes, guilds and confraternities of the city. When it arrives at its destination, it is exhibited to the people. After a period of prayer, the dried, clotted blood begins to liquefy. When I saw it, the blood actually increased in volume, so that the sealed vessel, which was less than half full when the blood was dry, was almost completely filled after the liquefaction occurred.
The miracle of liquefaction is attested to since at least 1389 - over 600 years. In that time, no one has been able to give a satisfactory explanation for the liquefaction.
St. Alphonsus Liguori wrote regarding Saint Januarius:
"The Neapolitans honor this saint as the principal patron of their city and nation, and the Lord himself has continued to honor him, by allowing many miracles to be wrought through his intercession, particularly when the frightful eruptions of Mount Vesuvius have threatened the city of Naples with utter destruction. While the relics of St. Januarius were being brought in procession towards this terrific volcano, the torrents of lava and liquid fire which it emitted have ceased, or turned their course from the city. But the most stupendous miracle, and that which is greatly celebrated in the church, is the liquefying and boiling up of this blessed martyr's blood whenever the vials are brought in sight of his head. This miracle is renewed many times in the year, in presence of all who desire to witness it; yet some heretics have endeavored to throw a doubt upon its genuineness, by frivolous and incoherent explanations; but no one can deny the effect to be miraculous, unless he be prepared to question the evidence of his senses."
John Henry Cardinal Newman (now Blessed) also attested to the veracity of the miracle of liquefaction:
"I think it impossible to withstand the evidence which is brought for the liquefaction of the blood of St. Januarius at Naples and for the motion of the eyes in the pictures of the Madonna in the Papal States."