Modernization

Falkayn stayed in Castle Afon in the sacred Old Quarter of Ardaig where there are gray stone buildings with fantastic turrets and battlements. See here. By Flandry's time, there have been at least three major changes:

Castle Afon is now occupied not by the Hand of the Vach Dathyr but by the Roidhun of a unified Merseia, who is elected from among the landless Vach Urdiolch;

most government business has moved to the new co-capital, antipodal Tridaig;

however, Brechdan Ironrede, Hand of the Vach Ynvory, Fleet Admiral in the Merseian Space Navy and Protector of the Roidhun's Grand Council, has had the new Navy office block, Admiralty House, built in Ardaig.

The shadow of the new tower's gleaming tiers engulfs Afon while aircraft swarm around the tower's beacon-topped upper flanges like seabirds. Although Admiralty House clashes with the modern skyline around the bay, it is a culmination of "...the battlements, dome roofs, and craggy spires of the old quarter." (Young Flandry, p. 90)

The location of Admiralty House in Ardaig is convenient because it is close to the Ynvory Castle Dhangodhan but it is also appropriate:

"...that the instruments of Merseia's destiny should have roots in Merseia's eternal city." (p. 89)

No city is eternal but they can seem that way.

Gaius Julius Caesar: Rome is the mob.
Marcus Licinius Crassus: No! Rome is an eternal thought in the mind of God.
Caesar: I'd no idea you'd grown religious.
Crassus: [laughs] It doesn't matter. If there were no gods at all I'd still revere them. If there were no Rome, I'd dream of her.
-copied from here.

I thought that Crassus said "...in the minds of the gods..." but this is the dialogue as I have found it on google. The Terran Empire is modeled on the Roman Empire and the Merseian Roidhunate is the rival of the Terran Empire. It is appropriate to quote the dramatic characters, Caesar and Crassus. Young Flandry, when he is older, will meet their Terran equivalents.