As RedState reports, President Donald Trump's administration has announced that within two weeks it will begin excavating the foundations of the work it calls the Great Triumphal Arch and Military Observation Deck, 250 feet high, at Memorial Circle on Columbia Island, between the Lincoln Memorial and Arlington National Cemetery. It says the work will be a spectacle for visitors, a post for snipers and drones to guard the city, and, finally, a monument befitting the capital of the most powerful state. On 31 October, however, the District of Columbia and Virginia asked a federal court to halt the work: the arch, they say, is unlawfully tall, will snarl traffic for years, and the whole project is flagrantly unlawful. The Washington Post, having built a three-dimensional model, is said to have found that the arch's shadow falls on many graves and monuments, and on some days even on the grave of John F. Kennedy and its eternal flame; the administration answers that most of the shadows fall in the early morning, before the cemetery opens. On 30 October Judge Tanya Chutkan, in a separate suit whose plaintiffs RedState does not name, indicated that she might halt the work at least for a time, and asked whether the president simply wished to dazzle the city.

"All these must be built with due regard to soundness, usefulness and beauty." Of soundness the reports say nothing at all: nothing of foundations laid on an island in a river, nothing of materials, nothing of the architect. What is said of usefulness does not offend me, who prepared ballistae and scorpions for Caesar: to set a lookout on a high place is a military matter, and an honourable one. But propriety requires that a building's form arise from its use. An arch is a gate of honour, through which the victor passes with his army; a watchtower is a tower from which sentries look out. Whoever joins the two in one work makes neither a whole gate nor a whole tower; and to station marksmen in a triumphal vault is like building an armoury inside a temple.

Of the site I must speak more gravely. An architect ought to know astronomy, so that he understands how the sun runs through the months and where shadows fall. The RedState writer wittily reminds us that the sun moves. True, the sun moves; but that is why the architect has a gnomon, to know where it moves. This question belonged not in the forum or before a judge, but on the drawing board, before the first spade touched the earth. And Arlington is the resting place of soldiers who fell for their country; a monument that claims to honour them ought not to overbear them, but to agree in modest proportion with the works around it, as the members of a body answer to one another.

As for the District and Virginia, neighbouring magistracies, I see that they go to law late, a few days before the digging, and use that delay as a courtroom weapon, not as a rule of the craft. I grant it: every community should use its own laws, and our Augustus fixed by public law the heights of buildings in the city, a law that bound even the princeps. But if a height law exists, it should have been produced years ago, not on the eve of the Kalends; and if none exists, it is unjust to forbid an arch by lawsuit in place of law. Both sides, then, share one fault: to begin a great work without a finished public plan, and to fight it without a finished argument.

There remains the greatest matter, on which the reports are wholly silent: what it costs, who pays, who builds. "In the famous and great Greek city of Ephesus an ancient law is said to have been laid down by the ancestors, harsh in its terms but not unjust in principle": an architect who took on a public work declared its price in advance and pledged his property; if he spent more than a quarter over, he paid it from his own purse. The remedy is ready to hand: let the architect be named, let him declare the price, let him pledge his goods; let the shadows, measured by gnomon through the whole year, be publicly posted; then let it either be built of stone for the ages, or not be built at all. He who cannot measure the shadow of his own work should not raise an arch.