John Lenthall (d. 1808) was born in Chesterfield, England, and trained as a carpenter. About 1793, he moved to the United States, becoming one of the early residents of the Federal City. He married Jane King, the daughter of Robert King, Sr., then the chief surveyor for the City of Washington, and eventually became friends with Benjamin Henry Latrobe, who hired him as clerk, or chief foreman, of the public works. Latrobe’s long absences from Washington required Lenthall to assume management over most aspects of the project. On 19 Sep. 1808, Lenthall was crushed to death when the vault of the court room in the north wing of the Capitol collapsed. In a eulogy composed the following day, Latrobe described Lenthall as “a perfect master” of his trade and praised his “benevolence of heart,” while also noting Lenthall’s “reserved exterior” and “rigid adherence to his own principles and opinions which nothing could bend” (National Intelligencer, 23 Sep. 1808; Latrobe, Correspondence description begins John C. Van Horne and Lee W. Formwalt, eds., The Correspondence and Miscellaneous Papers of Benjamin Henry Latrobe, New Haven, 1984–88, 3 vols. description ends , 1:256n; Benjamin H. Latrobe to TJ, 23 Sep. 1808).

As a measurement for stone, perches were understood to equal 16½ feet in length, 18 inches in height, and 12 inches in thickness (OED description begins J. A. Simpson and E. S. C. Weiner, eds., The Oxford English Dictionary, Oxford, 1989, 20 vols. description ends ; Carl R. Lounsbury, An Illustrated Glossary of Early Southern Architecture and Landscape [New York, 1994], 267). After consulting with Lenthall, TJ had asked Latrobe in his letter of 23 Apr. to have Lenthall report on the perches of stonework laid every week.