Culverts and aqueducts both allowed streams and rivers to cross uninterrupted below the C&O Canal. Aqueducts were usually larger—more like bridges. But what else differentiates a culvert from an aqueduct? The debate rages on at mile marker 31.9 where Broad Run enters the Potomac.  A double culvert was originally built to accommodate the spring, but then a wooden trunk was constructed to support the Canal bed over the stream. Although the customary arches were not present, Canal archeologist Thomas Hahn was satisfied that the structure included enough features of an aqueduct to label it as such. Culvert? Aqueduct? You be the judge.