DovBear: Lag B'omer thoughts: "Those of you who oppose Yom Hazikoron observances like the siren, on the grounds that this is not a Jewish practice are required to oppose the practice of lighting bonfires on Lag B'omer.
Bonfires were known in Christian Europe as a way to honor Chirstian saints as far back as the tenth century. They don't appear as a Jewish practice until the 16th century.
Christian scholars say that this practice of celebrating saints with bonfires is traced to pagan, pre-Christian practices, which were later adapted by the local people to Christianity. Indeed, the Celtics made bonfires to honor some of their deities and spirits. No one would ever claim that these Celtic practices, going back into old England, were originally of Jewish origin.
The Lag B'omer bonfire is every bit as foreign as the siren. If one is out, so is the other."