How was Saint Valentine put to death?

The one fact that can be stated confidently is that we know nothing about the legendary Saint Valentine, not even whether he actually existed. Wikipedia says that it is uncertain whether St. Valentine is to be identified as one saint or the conflation of two saints of the same name, which if true would militate against any tradition that he was imprisoned or executed on a particular day. Nevertheless tradition says that he died on February 14, 273 on Via Flaminia in the north of Rome. When, in 496, Pope Gelasius included Valentine among all those "... whose names are justly reverenced among men, but whose acts are known only to God," Gelasius implies that, in his time, nothing was known about the life of Valentine. Subsequent tradition speaks of St. Valentine being arrested for secretly marrying young couples so that the husbands could avoid military service. This tradition usually asserts that Saint Valentine was tortured and beheaded.