Treaty of Maastricht (1843)

The Treaty of Maastricht, signed in 1843 by Belgium and the Netherlands four years after the Treaty of London established Belgian independence, finally settled the border between the two countries. 
Border enclaves.
Inability to decide a clear line of demarcation in Baarle-Hertog resulted in the division of the disputed territory into 5732 separate parcels of land. These formed part of a very complicated frontier which sometimes passes through houses, and has tiny enclaves, due to land ownership dating back to the 12th century. Belgian enclaves in otherwise Dutch territory even have at times Dutch counter-enclaves within them.
Part of the left bank of the Meuse, near Maastricht, came back to the Netherlands.