While there is this romantic story about Charlemagne hesitating which hinges on vague notion without proof that Charlemagne did say that he was not aware that the Pope Leo the III was going to coronat him, had he known he would not have come to the Basilica. There is no evidence to this. Historians view is actually he knew quite well that the coronation was going to take place and he accepted with gusto. That said there were some clear risks associated with the coronation from his vantage point that most likely had to consider. That may have caused for Charlemagne to perhaps think it through a little bit in private. See the explanation… Bottom line, history does not support the hesitation hypothesis, the most likely scenario is he thought it through carefully, he accepted the coronation with his eyes wide open.
While there is this romantic story about Charlemagne hesitating which hinges on vague notion that Charlemagne said that he was not aware that the Pope Leo the III was going to coronating, there is no evidence to this. Historians view is actually he knew quite well that the coronation was going to happen. That said there some clear risk points that may have caused to perhaps Charlemagne to perhaps think it through a little bit. Here is my opinion of what his thoughts may have been: 1) How would the Frank Nobles will take this, what is the risk of unintentionally sending the wrong message to the Franks. After all he was the king of the Franks. 2) The idea of Rome “Pagan” or “Christian” was still not that popular with the Franks. After all just like the rest of the german tribes they spent centuries being bullied by Rome. So what is the value of the Holy Roman Empire what does it buy him? 3) Byzanteum had a woman Empress Irene, and clearly Charlemagne need to consider How Iren of Constantinopolis will view this coronation. Most likely illegal in her eyes, what is the consequence? Is Charlemagne opening yet another flank with all the fighting going on on his realm. While Charlemagne at this time was at peak of his power he may not have wanted to extend himself to Byzantium, certainly not go at war with a legitimate Roman power center such as Constantinopolis. Indeed right after coronation he did not wait too long to send an invitation for marriage to Irene. This actions, were indeed actions of an Emperor that was well aware of his coronation, and its potential pitfalls, thus the marriage invitation as a mitigation strategy 4) What was Pope Leo III motive to coronate Charlemagne knowing he was not the legitimate Roman line. Obviously Charlemagne knew that Leo III wa not doing this out of kindness of his heart, rather to establish the Papacy and himself as power broker to empire building. Reaffirming the power of the Papacy and Leo III to coronate under ecclesiastical power. 5) This action had serious consequences for centuries to come establishing two centers of Roman power (Holy Roman Power if you prefer). One in the west with fluctuating centers across European powers with respect to secular power, but firmly anchored in Rome as center of ecclesiastical Power (also secular during the Papal Monarchy era 1200 to the fall of the papal monarchy in the 19th century). The other in Byzantium, with both the spiritual and secular power in Constantinopolis.