Muslims, of course. And iconoclast emperors.
Okay, let’s recap the status of All Saints’ feasts.
Back in the day, the celebration of all the martyrs not otherwise celebrated, or all the saints not otherwise celebrated, usually took place in the spring. In Edessa, it was on May 13, from AD 320 on. In Lebanon and Syria, you have celebrations in Lent, or on the first Thursday after Easter from 411 on, a celebration of all martyrs. In Antioch (from the days of Ss. Ephrem and John Chrysostom) and in Wurzburg, All Saints (ton Hagion Panton) was the first Sunday after Pentecost. In the West, it was on April 20.
When the Pantheon in Rome was turned into the Church of Sancta Maria ad Martyres in 609, the building was dedicated on May 13, and Rome began celebrating All Saints’ Day on May 13. There was some spread of the new date, but it was all voluntary changes. Rome did not push it on other areas. Ireland, for one, still celebrated on April 20. But it was a big feast, and Pope Sergius I wrote a long litany in Greek for it in AD 690.
And then, in 731 in Rome, the date changed again.
It was a sad time in Church history. Emperor Leo III, Leo the Isaurian, was a skilled general and governor from Syria, who had overthrown Theodosius III with the help of other military officials. His strong governance had brought peace to the Empire and driven back the Bulgars and Muslims. But he had also brought in forcible Baptism of Jews and Montanists, and then decided that he could smoothe things over with the Muslims by scrubbing Christianity of images and saints. He declared icons illegal in a series of laws that came out from 726-729. Much of the aristocracy supported him, but most theologians, monks, and normal laypeople hated it.
Over in the West, people just ignored Emperor Leo’s dumb edicts. In the East, people who defied the new laws got punished — or they got the heck out, moving to places like Rome with less economy and more freedom. Ironically, one of the strongest voices against Emperor Leo was St. John of Damascus — who lived in Damascus and other places in the Muslim caliphate, and thus could not get silenced by Emperor Leo.
Emperor Leo III also had a feud going with Pope Gregory II. In 722 (the year of the forcible baptisms), the Emperor demanded more tax money and tax food from Rome and the papal estates, because there were war expenses. But Rome was having trouble feeding its own people, and had no surplus money or food to send. The imperial governor got insistent, and the Roman populace threw the rascal out. (And the Pope didn’t object or anything.) Since imperial forces in Ravenna were busy holding off the Lombards/Longobards, and since Emperor Leo was too busy to send troops from elsewhere, the Romans got away with it.
In 725, Emperor Leo sent a new guy, Marinus, to be Dux of his Roman lands. Things might have smoothed over, but Marinus made a serious attempt to put a hit on the Pope. He got recalled, another guy was made Exarch of Ravenna, and the plot continued. It got discovered, the plotters talked, and nobody in Rome loved Constantinople.
Then the iconoclasm laws came along. The East says that Gregory II excommunicated the Emperor. The West says that he sent some strongly worded letters telling the Emperor to butt out of religious matters, and that iconoclasm was evil and stupid. Emperor Leo sent a new Exarch, who started a new plot to kill the Pope and the major notables of Rome. This plot got discovered, too. The Exarch then made a deal with the Lombards to attack Rome as a joint force, but the Pope managed to get the Lombards to change their minds. Gregory stayed openly courteous to Exarch Eutychius, and helped him fight off a non-religious revolt. Eutychius was grateful, and things were looking up. Then Gregory II died on February 11, 731. He was later declared a saint; his feastday is on February 13.
Since he was such a saintly guy and had led the fight against iconoclasm, a lot of people showed up for Gregory II’s funeral. One of them was a Syrian priest, Gregory son of John. He seems to have been something of a scholar and a holy type of guy, but he must have really made an impression.
Because on February 22, 731, this visitor to Rome got elected Pope. By acclamation of the people of Rome.
He was so flabbergasted that he followed an old custom, and asked permission from the Exarch of Ravenna. (Because he was from the East, where bishop was more of a government bureaucratic position.) It was granted, and he was consecrated bishop and Pope on March 18. (No telling what his old bishop thought about it.) He was the last pope until Pope Francis to have origins outside of Europe.
Pope Gregory III started things off with a bang, by sending nice letters to the exiled/deposed Patriarch of Constantinople, and nastygrams about iconoclasm to Emperor Leo III. The emperor put the pope’s messenger in prison.
Pope Gregory III doubled down. He put up a full ikonostasis at the base of the two-story main altar structure of the old St. Peter’s Basilica. He called a synod against iconoclasm and for devotion to Mary and the saints, to be held in November 731. And he also ordered a new oratory to be built in the main nave, all the way down front, and just to the left of the doors going to the main altar. The oratory featured two altars (one honoring Mary, the other St. Gabinius) with a big arch covering them, and a consolidation of saints’ bodies and relics, buried all around the floor and under the altars. And with images and statues, of course!
On November 1, 731, just before the start of the synod against iconoclasm, the new oratory was dedicated. Pope Gregory III announced that from now on, the feast of All Saints in Rome would be celebrated on November 1. (Which of course made the eve of the feast a time for fasting, prayer vigils, and whatever stuff you do to stay awake during fasting and prayer vigils.)
Emperor Leo III sent a fleet to punish Rome, but it was wrecked.
The new date of the feast was still promulgated by free choice; but a lot of kings and missionaries were interested in it because it was a blow against iconoclasm. (And overbearing Byzantine emperors.) Ireland doesn’t seem to have picked up the new date for a long time.
Pope Gregory III reigned until his death on November 28, 741. (He and Emperor Leo III died in the same year.) He was buried in his oratory of Mary and the saints. Unlike Leo, Pope Gregory III was later declared a saint, and his day is December 10.
So there’s no Celtic pagan holiday. The reason we have Halloween is an emperor who was soft on Muslims and hard on icons, and a Pope who fought back.
Everything else is just decorations and candy.
* Other achievements by Pope St. Gregory III — Appointed St. Boniface the archbishop of Germany, and a papal legate, in order to support missionary work among German pagans and lapsed Christians. Founded and perpetually funded a hospital for the poor, dedicated to the Eastern Ss. Sergius and Bacchus. Founded a monastery in Rome named St. Chrysogonus. Restored Rome’s walls. Built, restored, re-roofed, and decorated many churches in Rome. Put a lead roof back on the Pantheon. Helped recapture Ravenna from the Lombards.