The Pompey Stone was discovered in the early 1820s, and was believed to be hundreds of years old. It turned out to be a hoax, but a fairly benign one.

Research:

• Barber, John Warner and Henry Howe. “Historical collections of the state of New York : containing a general collection of the most interesting facts, traditions, biographical sketches, anecdotes, &c. relating to its history and antiquities, with geographical descriptions of every township in the state ; illustrated by 230 engravings.” New York : S. Tuttle. 1841. https://archive.org/details/historicalcollec01barbg/
• Beauchamp, W.M. “The Pompey Stone.” The American Antiquarian and Oriental Journal April-June 1911: Vol 33 Iss 2. https://archive.org/details/sim_american-antiquarian-and-oriental-journal_april-june-1911_33_2/page/7/ 
• Clark, Joshua Victor Hopkins. “Onondaga, or, Reminiscences of earlier and later times : being a series of historical sketches relative to Onondaga, with notes on the several towns in the county, and Oswego.” Syracuse, N.Y. : Stoddard and Babcock. 1849. https://archive.org/details/onondagaorremini00clar/
• Conlon, John Thomas. “The Beginnings of Catholicism in New Netherland.” United States Catholic Historical Society 1933: Vol 23. https://archive.org/details/sim_united-states-catholic-historical-society-records_1933_23/page/171
• Crowell, Kathy. “Early Development of the Town of Pompey.” Dwight H. Bruce (ed.), Onondaga's Centennial. Boston History Co., 1896, Vol. I, pp. 595-608; 627-631.. https://onondaga.nygenweb.net/POMPEY/EARLYDEV.HTM
• Homes, Henry A. “The Pompey (N.Y.) Stone with an Inscription and Date of A.D. ” Transactions of the Oneida Historical Society at Utica. 1881. https://archive.org/details/transactionsofon00onei/page/83/mode/1up
• Huguenin, Charles A. “The Pompey Stone.” New York Folklore Quarterly. Spring 1958: Vol 14 Iss 1. https://archive.org/details/sim_new-york-folklore-quarterly_spring-1958_14_1/
• O’Connor, Thomas F. “An Alleged Spanish Entrada into New York.” Mid-America : an historical review. Chicago, Ill. : Loyola University. 1943. https://archive.org/details/midamericahistor25unse/
• “Proceedings of the American Antiquarian Society at the Semi-annual Meeting in Boston, April 29, 1863.” Boston. John Wilson and Son. 1863.
• Schoolcraft, Henry Rowe. “Notes on the Iroquois, or, Contributions to American history, antiquities, and general ethnology.” Albany : E.H. Pease. 1847. https://archive.org/details/bp_1739112/
• Squier, E. G. “Antiquities of the state of New York; being the results of extensive original surveys and explorations, with a supplement on the antiquities of the west.” Buffalo, G. H. Derby. 1851. https://archive.org/details/antiquitiesofsta00squi/
• “The Pompey Stone.” Harper's Weekly 1879-12-20: Vol 23 Iss 1199. https://archive.org/details/sim_harpers-weekly_harpers-weekly_1879-12-20_23_1199/page/983/mode/1up