It was that confounded scribe’s fault.  Well, perhaps it was his fault as well, just a little bit, for he hadn’t bothered telling the scribe and he didn’t think anyone would care.  He didn’t know that one of the Brandybucks would actually bother cross the river into the real Shire to attend his accession party.  There the Yellowskin was, lying in the open, and the Brandybuck actually jabbed a grubby finger at it and demanded to know why the Yellowskin seemed to be ignoring the fact that the Brandybucks had held the title of Thain first, for a very long time, thank you very much, and pretending that it originated with the Tooks was a slap in the face.

To which Isengrim had replied (he should have noted, in retrospect, that this was after a few Southfarthing reds) that if the Brandybucks cared that much, maybe they shouldn’t have given up the title.

“We didn’t give it up,” the Brandybuck replied.  “You took it from us.”

“Because the Brandybucks—sorry, Oldbucks—were embroiled in scandal and someone had to take charge in case we ever needed a muster.”

“We haven’t needed one since the days of the King.”

“In which case, why should you care if the Tooks hold it?”

“I don’t care if the Tooks hold it, they just ought to know that the Brandybucks held it first!”

The Brandybuck must also have been having a bit too much Southfarthing red.  Isengrim’s wife walked over, laid her hand on his arm, and begged him not to start his Thainship with such animosity.  Isengrim reluctantly turned away, but not before he heard the Brandybuck’s parting shot:  “You know, if you’re going to try and deserve your title, the least you could do is have a slightly grander home.”

Isengrim knew exactly what he was talking about—Gorhendad, after surrendering (though the Brandybucks always said ‘bestowing’) the title of Thain on Isumbras, deliberately moved to Buckland so that he wouldn’t be exiled there, claiming that he preferred the wilds of Buckland to the stiff-neckedness of the Shire proper.  (Not, Isengrim thought, that he would have been—but the threat was real enough and his neck was stiff enough that he moved nonetheless.)  Consequently, he set out to build the biggest smial that had ever existed, as an eyesore to mock any Took unfortunate enough to leave the Shire by way of Bree.  And things had rather stayed the same from that point forwards.

Isengrim hated to admit that he was rising to the bait, but he had always had a bit of an architectural mind and, provided the rock was stable, he had just the hill in mind.  Stairs indoors?  Yes, they’d have stairs.  A ballroom, too, with a high-vaulted ceiling, and he knew the Brandybucks didn’t have that.  By the time the night was over he had the entire thing, down to the privies (he had a few inventive cousins who had been itching to try out a better plumbing system).  Now, he just had to try and persuade the wife…

A/N: A careful examination of Appendix C explains the chronological inconsistency that Dreamflower drew my attention to.  I'm betting that those particular trees were copied from Brandybuck records.

Stairs in the Great Smials are documented--otherwise Lalia the Great would never have had anything to fall down.  Elanor Winterflowers has argued cogently for the existence of stairs inside Brandy Hall as well.  The ballroom is entirely Dreamflower's invention, and I can only hope that its inclusion here tickles her fancy.