When the channel for the C&O Canal was being dug in 1837, argillomagenisian limestone was discovered – material well suited for hydraulic cement. Having the ability to manufacture cement close to the job site was hugely beneficial ; therefore, the C&O Canal Company authorized George Shafer to construct a cement mill in 1838 at the foot of Roundtop Hill. This mill supplied cement to Roundtop Hill, up to the Paw Paw Tunnel, and as far away as the Washington Monument, the Cabin John Bridge, and the U.S. Capitol. Cement was packaged into barrels and sacks and shipped downstream by both the C&O Canal and the B&O Railroad.

In 1863, the mill was sold and renamed the Round Top Hydraulic Cement Company. It continued as a booming industry, averaging 2,100 barrels of hydraulic cement per week, making it one of Washington County’s most profitable businesses. Over 100 locals workers operated the mill, which included a 16-foot-diameter overshot waterwheel, four pairs of grind stones, and eight coal-fired cement kilns.  The cement mill was relocated to the berm side of the canal – meaning it no longer got power from the fall of water from the canal. It was most likely converted to steam power as a chimney sits upon the present-day ruins. The mill was put out of business by Portland cement – which was stronger and took longer to harden – and closed in 1909. Although the landscape has changed and the people are gone, the mill ruins still echo with signs of past commerce, prosperity, hard labor, and industry.