Moorglademover writes "The Rod of Smiting (as appears in the 1E DMG) is essentially a +3 mace or club with an unusual power; if the attacker rolls a natural 20 to hit with it on a golem, the golem is destroyed, and it also has a bonus against creatures from the lower planes. Why?
The Staff of Sejanus
By: Moorglademover (firstname.lastname@example.org)
(Used with Permission. Do not repost without obtaining prior permission from the author.)
It appears that all Rods of Smiting are in fact lesser copies of a long-lost magical item, the Staff of Sejanus. Sejanus was a high priest of the Aerdi tribe, when they were starting to expand and develop their territory in what would become the Great Kingdom. At that time, the lands in question were under the rule of Baron Lum, creator of the eponymous Machine, and his general-priest henchman, Leuk-O. Leuk-O is (in)famous for his Mighty Servant, a giant demon-powered automaton that was the primary method of the enforcement of the rule of Lum and Leuk-O. After the passing of Lum, Leuk-O became the tyrant of myth and legend, and his followers grew crueller and more despotic with each passing day.
The Aerdians, along with several other tribes, had determined that the tyranny of Leuk-O must be stopped. But the Mighty Servant was too powerful for the opponents of Leuk-O. Even its appearance was enough to send most troops scattering to the four winds, and in actual battle it seemed unstoppable.
At this point the High Priest of Pholtus within the Aerdian people, a man named Sejanus, called a secret meeting. Heironeous himself had appeared to him, he said, and had revealed to him a vision of how the Mighty Servant, and Leuk-O, might be defeated. By dint of oratory and persuasion, he convinced the High Priests of Hextor, Heironeous and Zilchus to work with him in the creation of a symbol of the power of the gods of the Aerdi, and the authority that they commanded. Indeed, he also induced the high mages of the Aerdi to assist him. For three days and nights they chanted, prayed and laboured. Spells and rituals were completed, and libations and sacrifices made.
The end result was the Staff of Sejanus. Fully six feet long, made of bronzewood and steel, the Staff would have the divine power to be able to counteract the effects of the Mighty Servant. The symbols of the three gods were inscribed in an intertwined fashion around the body of the Staff, and atop them all was the crest of the people of the Aerdi, wrought of gold and jewels. More meetings and secret councils took place, and eventually the time came for the Aerdi to throw off the yoke of Leuk-O and his followers.
The army of the Aerdi and their allies encamped at one of their strongholds, Garwad Keep. Trusting in the might of the Staff to protect them, they deployed their troops around the hill upon which the Keep stood, and waited for Leuk-O to arrive. They did not have to wait long.
The army of Leuk-O was considerably smaller than the army of the Aerdi, for in their hubris they trusted in the power of the Mighty Servant and Leuk-O, riding atop the giant, to crush the rebellion. Leuk-O made the Mighty Servant stride into the middle of the field of battle, and contemptuously ordered the leaders of the rebellion to submit to his rule; then he would spare some of their followers.
Instead, a white-bearded man walked out to meet him, using a staff to support him. "Your tyranny is ended, and nevermore shall the Aerdi bend their knee to any other!" So saying, Sejanus plunged the Staff deep into the oerth, and with one fist clenched around the Staff, placed his other palm against the Mighty Servant.
A deep, bell-like tone emanated from the Staff, and started to resonate deep within the inner workings of the Mighty Servant. Black, oily smoke began to issue from inside, and small arcs of lightning began to coruscate around the head and shoulders of the giant, where Leuk-O's throne was positioned. Finally, while horrible screaming could be heard from both without and within the automaton, the whole scene exploded in a flash of light and a crack of thunder.
When the smoke cleared, nothing was left of Leuk-O, the Mighty Servant, or Sejanus. Only the Staff remained, its steel blackened and tarnished, its wooden shaft scorched, and its headpiece cracked and dulled. With a great shout the host of the Aerdi charged their now-dismayed oppressors, and with their victory in battle the freedom of the Aerdi was won, and their ascent to greatness begun.
After the battle, the Staff was taken back to the priests who had helped to create it, and the Staff of Sejanus was given to the High Priest of Pholtus, pre-eminent in the gods of the Aerdi, to serve as the supreme symbol of office, and to be passed down to his successor when the time came. Its eventual loss is another story, but since that time the leaders of the Aerdi churches have had sceptres of power and authority made to mirror the original; the Staff of Sejanus.
Note: Aerdy, Great Migrations, Prehistory"