Until recently there was a frieze around the lobby of the Hotel Pontchartrain in downtown Detroit, a naively charming painting of a forested lakefront landscape with Indians peeping out from behind the trees. The hotel was built on the site of Fort Pontchartrain du Détroit, the old French garrison that three hundred years ago held a hundred or so pioneer families inside its walls while several thousand Ottawas and Hurons and Potawatomis went about their business outside, but the frieze evoked an era before even that rude structure was built in the lush woodlands of the place that was…