Salt marshes are built by tidal action and sedimentation in estuaries where river and sea flow together, and they are thus among the most ordinary landscapes in the world. With wide, flat horizons unmodulated by hills or trees and undecorated by wildflowers, they are anything but spectacular. Moreover, the marsh's spring and summer miasma was long believed to be a source of disease. Salt marshes were rarely frequented by American artists of the last century; artists were more inclined to brush sermons about Manifest Destiny and the Transcendental spirit into their grandiose landscape paintings of the mountains, waterfalls, and rivers of the Northeast, the Rockies, or the imposing Great Plains. Yet, during the last forty years of his life, Martin Johnson Heade (1819–1904) obsessively, ritualistically painted views of salt marshes along the eastern seaboard. He was unique among painters in his devotion to this theme. Though he, too, painted the landscape as cultural oratory, his message differed from the celebratory recitals of his peers, and he did not attract their audience.