The unction served as a reminder of the baptism of king Clovis I in Rheims by archbishop Saint Remi in 496/499, where the ceremony was finally transferred in 816 and completed with the use of the Holy Ampulla found in 869 in the grave of the Saint. Since this roman glass vial containing the balm due to be mixed with chrism, was allegedly brought by the dove of the Holy Spirit, the French monarchs claimed to receive their power by divine right.
http://en.wikipedia.org/wiki/Coronation ... ch_monarch