Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
aggĕrātĭo (adg-), ōnis, f. [1. aggero], a heaping up; in concr., that which is heaped up, a mole, dike (not before the Aug. per.): naves supra adgerationem, quae fuerat sub aquā, sederunt, Vitr. 10, 22, 263; Just. 2, 1 fin.