Our Division, the First, was reviewed this forenoon by General Grant and Maj. Gen. J. A. McClernand. While the review was in progress three men were seen on the roofs of two small log houses at the southern end of Jones' Field, taking notes on our maneuvers, the number of men in line, etc. They were dressed in butternut suits although, it is said, they had claimed to be Union men; yet when the review was ended no trace of them could be found.
Source: Alexander G. Downing, Edited by Olynthus B., Clark, Downing’s Civil War Diary, p. 39-40