The Aa () is a small river in the Netherlands. It rises near Nederweert in the southeastern province of Limburg, in the Peel region. It flows northwest through the province of North Brabant towards 's-Hertogenbosch, roughly along the Zuid-Willemsvaart canal. In 's-Hertogenbosch, at the confluence of the Aa and the Dommel, the river Dieze is formed, which flows into the Meuse () a few km further. The main cities and towns along the Aa's course are Asten, Helmond, Veghel and 's-Hertogenbosch. History The old Aa was navigable The current Aa is not as important as the former river. This is due to the Zuid-Willemsvaart, which has been dug in the drainage basin of the Aa from 1823 to 1826. The canal absorbs much of the water that would otherwise flow to the Aa. The Zuid-Willemsvaart was initially dug to be much wider than the Aa, but since then its width and depth accelerated, taking ever more water from the Aa. The role of the Aa in history can only be understood by considering its former state. In the 1760s the Aa was navigable till the bridge of Erp, about 25 km from 's-Hertogenbosch. In 1839 it was still navigable till the lock of Erp. There are also reports that barges moved by poles and small boats could navigate the river till Koks, just north of Gemert, about 30 km from 's-Hertogenbosch. All this might actually point to the same place. Anyway, near the Koksehoeve in Koks, Gemert there was a harbor for barges to and from 's-Hertogenbosch, and this activity only ended after the Zuid-Willemsvaart was dug. It explains why Heeswijk Castle on the Aa, about 10 km from 's-Hertogenbosch, was such a strategic position for defending 's-Hertogenbosch against the Dutch Republic. Plans to dig a canal In 1625 plans were made to make the Aa navigable from the Stipdonk mill at Lierop, south of Helmond to 's-Hertogenbosch. The idea was that peat and firewood from the Peel could then be moved more cheaply to 's-Hertogenbosch. In 1626 agreements were made with municipalities along the river, and in 1627 and 1628 locks were updated, and the Aa was brought to depth in some places. The 1629 conquest of 's-Hertogenbosch by the Dutch Republic cancelled this development. When the Batavian Republic was founded in 1795, these plans were again considered. The first plan aimed to make the Aa navigable till Veghel.