This site is dedicated in memory of Rabbi Gavriel and Rivka Holtzberg who were murdered at their Chabad House in Mumbai. This is the place to learn more and ask those questions you were always too shy to ask.
"The requirement is to place the Chanukah light by the doorway of one's house, from the outside." (Shabbat 21b)
Rashi writes that this is because of pirsumei nisa - to publicize the miracle. Why do we stress this on Chanuka? The Greeks endeavored to detach the Jews from Torah study. However, they did not suffice with this evil plan, but also demanded that the Jews write on the horn of the ox that they were denouncing their share in the G-d of Israel (Midrash Rabbah, Bereishit 2:4).
They made the strange request that the Jewish people use the horn of the ox because in those days it was customary to travel on wagons and chariots which were driven by oxen. The oxen would span the roads and go from place to place, and the horn is the most prominent and visible part of the ox. Therefore, they demanded that their denial in Hashem be written on the ox's horn so that it would receive the widest publicity possible.
To counteract this, our Sages required that when we fulfill the mitzvah of lighting the Menorah, which commemorates the miracle Hashem did because of our allegiance to Him, it is to be done so as to attract the most public attention possible.