I believe that the English would have used the Clare spelling of his name. But then in France it would be Clair as you say.
I have been thinking about this idea of the St. Clairs guarding the gateways. Are we thinking that they were guarding Normandy's gateways against the King? Maybe we should consider thinking like a Viking and not a Scotsman. The Scots had had a long history with England and indeed needed to protect themselves from the English. But I don't think that Rollo had this history with the rest of France and now he was married to the King's daughter which almost guaranteed their safety. So the question is why did he locate his residence so near the eastern border?
Viking threats had come from the West before. Was Rollo confident of agreements with other Vikings to not raid his territory now. Or did he have a good captain (his son Wm. Longsword perhaps) with plenty of strength deployed along the coast that discouraged them? But in 914 Vikings attempted to create another settlement in Brittany. Finally in 935 the Bretons drove them out. This virtually ended Viking activity on the Continent. Only Frisia on the main Viking route was still raided regularly. The Historical Atlas of Vikings says: Rollo was made Count of Rouen as the rulers of Normandy did not use the title "duke" before 1006. ....Rollo was granted further lands around Bayeaux in 924 and his successor William Longsword acquired the Cotentin peninsula in 933, but attempts to expand eastwards were defeated. It seems like Rollo didn't help Charles with this problem very well. So maybe Charles was more worried about internal problems than Vikings and wanted to keep Rollo closer to him.
Could it be that Rollo was keeping an eye on Paris and the political events there. If he were to have another son now, this child would be in line some day to be King of France. But here is another idea triggered by these words of Rollo (I think)....."My castles are my King's alone from turret to foundation stone but the hand of Sinclair is his alone."
Apparently when the treaty was signed, those castles and territories that he had over run were now Charles' again and Rollo in exchange had the stewardship of it all without doing battle to keep it. Rollo gave a pledge, an oath and in the ceremony whole-heartedly accepted King Charles as his leige lord. Now this meant a lot to a Viking. Loyalty was apparently the most valued personal trait. It was the characteristic that they sought out in one another and no praise could be higher. Here some examples:
1. When the Swedes went down through Russia, some of them were hired as
palace guards in Byzantium. The emperor could depend upon their loyalty
over any of his people and he rewarded them richly. This of course led to
jealousy, but that's another story.
2. When King Knut invaded England, Edward Ironsides was king. Earl Godwin
and family remained loyal to Edward even though he had no chance of winning.
Other Earls switched sides and sent their armies to help Knut. When Knut
became king he had the traitorous Earls killed even though they helped him, but reward Earl Godwin, his enemy, with land and much honor.
For this reason, it is difficult for be to accept that Saxon, Earl Godwin's son Harold had made a deal with Norman Duke William to help him become King of England. I know that this also brings up the fact (or was it a fiction of William's cousin who wrote the history?) that Harold had made a pledge in a holy place over the bones of the saints to help William. If he were a truly loyal person, he would put his loyalty to Edward above his personal pride of keeping his pledge untarnished, thus breaking the forced pledge to carry out Edward's desires and for the good of his country.
3. Now the idea of Sinclairs being used as guards at gates to different areas carries on this idea. Loyalty was a quality that the family firmly instilled in their children. Their loyalty was recognized by numerous countries as a desirable and marketable trait.
From all that I have read, from the time that Rollo became Duke, he was a
changed man...or did his conversion to Christianity make the change in him?
It's sort of like one day he said, "Well, I've been a terror long enough, now I'm going to be as good as I can be." And he did.
4. so perhaps Rollo placed himself on the edge of Normandy so that he could go quickly to protect his lord, the King of France. I do not have a good history of France but have picked up these little bits and pieces about what was going on then. At some point Charles the Simple was imprisoned. Pope John X confirmed the election of Count Heribert's five-year-old son, Hugh, as archbishop of Rheims. In return for this he secured the release of Charles whom Heribert had imprisoned. It would be interesting to know just what was going on at court from 911 to 933.