The Horror From the Bridge is a short story by Ramsey Campbell that appeared in his 1964 collection The Inhabitant of the Lake and Less Welcome Tenants. It is set in Clotton, part of Campbell's Severn Valley milieu, and is largely a pastiche of H. P. Lovecraft's "The Dunwich Horror".
Clotton is described a small town located where the river Ton flows into the Severn. Only a "few leaning red-brick houses... remain of the uptown section of the once-prosperous town;" the rest of the town was deliberately destroyed in 1931, for reasons explained in the story. The town's most noteworthy feature, also dating to 1931, is a "20-foot high concrete building...on the bank of the Ton", with an "eldritch sign clumsily engraved on each wall", carvings that "were blurred by moss and weather." Outside of Clotton is a "pit on a patch of waste ground on what used to be Canning Road, near the river," containing "roughly-cut steps, each carrying a carven five-pointed sign, which led down into abysmal darkness."
In 1800, a man named James Phipps, "a gaunt pallid-faced man, with jet-black hair, and long bony hands," moved into a house in Clotton on Riverside Alley. He was forced to leave his previous home in Camside "because his unorthodox scientific researches were distasteful to the inhabitants." In 1805, he married a woman from Temphill--whose name no one knew--with a "corpse-like pallor, who...walked with a peculiarly stiff gait." (Later we learn that a "monstrous coven" met in the "artificial caverns beneath the graveyards" in Temphill, where "newly corpses" were "reanimated by certain horrendous formulae," and these "living cadavers were taken as wives".) A year later, a son, Lionel Phipps, was born to the couple; the story pointedly notes that the offspring of the reanimated mates "would have primal powers which properly belonged only to alien deities." The elder Phipps was preoccupied with trying to release a "hidden primal race" that had been imprisoned below the Ton. After his death in 1898--when he was well over a century old--his work was carried on by Lionel.
Trying to thwart these activities was Philip Chesterton, a librarian at the British Museum who became suspicious when Lionel Phipps came to that institution in 1900 to consult the Necronomicon and the Book of Eibon. Chesterton took a job at the library of Brichester University to better keep tabs on the goings on in Clotton.
Finally, on September 2, 1931, Lionel Phipps is able to release three river monsters, servitors of the Great Old Ones. Reciting passages from the Necronomicon, and with the help of a local gun club, Chesterton is able to kill Phipps and two of the monsters, and imprison the third under fast-drying concrete--upon which were hurriedly carved representations of the Elder Sign.