Your review of “Byzantium: 330-1453,” the new Royal Academy of Arts blockbuster show in London (“Domes of Gold,” October 25, 2008), opens with Dimitri Obolensky’s term, “Byzantine Commonwealth,” to describe a region that formed a common cultural and religious rather than political space with Constantinople. Two things readily come to mind in this connection. First, that commonwealth was largely defensive in a hostile environment that could not be easily subjugated by any other means. Here, the arrival and rise of the Slavs coincided with the emergence of Venice as an ever-more ambitious rival. Not surprisingly, the Venetians and the Slavs vigorously conspired during the Fourth Crusade, culminating with the capture and sacking of Constantinople in 1204. In short, the Byzantine Commonwealth was always a shaky truce with jealous neighbors. Second, Obolensky’s term is now of increasing value to the Russians, who are doing their best to revive it among Orthodox Christians. As Istanbul is not to be had, they are now trying to shift the cultural and religious center to Moscow, the new Constantinople. Coined in 1971, the term has already found many a good use, but its future appears no less than golden.