A farmer in Belgium accidentally moved the France-Belgium border, resulting in Belgium getting more land area than France. The incident ended up making Belgium, the farmer's home country 1000 sq mt bigger, and France, 1000 sq mt smaller.
The farmer was driving his tractor, and was annoyed by a large stone on this way. He then went ahead and moved the stone. Unbeknownst of him, he moved the stone that marked the border between the two countries.
The stone markers have been around for over 200 years all throughout the France-Belgium border for a stretch of 620 km. This particular boundary stone was laid down in 1819 after the Treaty of Kortrijk.