Having said that, I think any further discussion not pertaining to Chinese records of the Crusades should be moved to the world history thread. However, it may take me a long while to post any response (like this one for instance) because my attentions are focused elsewhere at the moment.
Agreed -- the reasons for crusaders's success is beyond the original question.
I am a late-(and new)comer to this discussion (and this entire website -- absolutely fantastic!!), and find it very interesting from the perspective of a Byzantinist. A couple basic questions still jump out to me from the original issue --
The Seljuks would have identified their territory as "Rum" (Rome), but their leader was the Sultan -- would a Sultan have taken the same identification (I think it was transliterated in one of the first posts as "Gaisa") as a Caesar? Is there a possibility that it could be a Seljuk Embassy? The Seljuk state was set up in 1081 -- would this have been their self-proclamation embassy to get on the diplomatic map?
Pursuing the original trail of investigation, however, it does not make any sense to me for the ambassador in question to be Simon de Montefort -- it smacks of searching through an index for a name that can be transliterated similarly. The Byzantine Emperor hardly got the First Crusaders to give Nicaea back to them, let alone send them on far flung diplomatic missions; certainely not before the crusaders had even entered into their quasi-vassal relationship with him (Alexios I), which happened in 1095; the "franks" were horrible allies (almost universally) -- why trust them with this new, and touchy, diplomatic venture?
Though Emperor Alexios I's asking of the Pope for help is understood as symptomatic of a longstanding "Byzantine Crusade" against the Turks (or something like), it really was a particular request for a particular situation, not with the idea of a long standing offer of "come over and help us, all of you, sometime." For instance, from 1081-1095 the primary enemy for Alexios I were the Normans under Bohemond and his father Robert Guiscard who were constantly attempting invasion of the West Balkans through Dyrrachium. For instance in Anna Komnena(daughter of Alexios I)'s Alexiad
, Book 5.4, Alexios asks Suleiman
(cousin I think of Sultan Alp Arslan and founder of the Seljuk state of Rum) for help vs. the Normans (Franks). It was of course then this same group of friendly Normans who came over to "help" in the crusade, and who ended up setting up a kingdom around Antioch for the purpose of better defeating the Byzantines. In any case "help us against the turks" is very vague because there are a lot of turkish tribes who are at war with each other, some of whom the Byzantines are allies with and some not -- probably, because they were the most concerning "Turks" in the 1080s, it was the Patzinaks.
Melissenos himself seems to have been captured by the "Scyths" (who I take as the Turkish Patzinak tribe) roughly around 1090, Anna cites him as helping Alexios out from captivity by sending secret documents about the enemy.
In any case, what I really want to address is the problems around Melissenos sending an embassy to the Song in Kaifeng in 1081 as the Caesar under Alexios I. I don't know anything about dating issues in 11th century Chinese history, but I am going to assume 1081 is secure. Alexios took the capital (Constantinople) in April of 1081. In 1080 Nikephoros III Botaniates (1078-1081) is still Emperor. Alexios as a loyal general had been asked to stamp out the rebellion of Nikephoros Bryennios, which he did. Also in that year, Nikephoros Melissenos set himself up in Nicaea (Asia Minor, Turkey) and proclaimed himself to be Emperor ("clad himself in purple"); Alexios does nothing about this rebellion -- his sister Eudokia was married to Melissenos, and perhaps he realized it was the moment to make a move for the throne as well. In any case, Melissenos makes a proposal to Alexios in that same year of splitting the rulership of the Empire: Alexios in the West (meaning the Balkans) and Melissenos in the East (Asia Minor). Alexios says no, but that is because he is about to take the capital --he soon offers Melissenos the position of Caesar (second in the Empire), but then once Alexios is emperor he creates the position of "sebastokrator" to be higher than Caesar, which he awards to his brother, Isaac, thereby dropping Melissenos down to #3. Also in 1080 Suleiman had set himself up as Seljuk Sultan in Asia Minor; we also know that Melissenos appeals to him diplomatically in that same year, before Alexios takes over.
All of this together, it seems to me most probable that:
1) Once April 1081 had happened, why would Melissenos in his position of 3rd in the Empire be interested in, and be asked to, oversee and sponsor the resuming of official diplomatic relations with an Empire that the Byzantines had lost relations with for centuries? Wouldn't Alexios, trying to establish a new dynasty, be sure the embassy was proclaiming HIM as emperor, and not his so-recent rival?
2) If the Embassy arrives in Kaifeng in 1081 it does not necessarily need to have been sent in 1081.
3) Melissenos's position in 1080, and also his possible diplomatic options, make it much more likely that he would send towards China -- he makes an appeal to the Seljuks, why not try farther as well? He is effectively blocked from Balkan alliances by Alexios's position, so sending further afield in the East is perhaps the only option; and if he actually believes he can set up an Empire from Nicaea, it would be a typically intelligent Byzantine diplomatic move to get in touch with those who "have the back" of your nearest friend/enemy/ally/invader.
The figure of "the great official Nisiduling Simengpan" then, we should look for as an official in the circle of Melissenos and a part of the Byzantine elite in Asia Minor, but NOT part of the circle of Alexios Comnenos. Looking for a Western European answer is even further off the right track.