France in the Siege of Maastricht (1673). As a result of this, the fortress Sint-Pieter was built on the northern edge. Around 1765 the skull of a Mosasaurus was discovered here in a limestone quarry, one of the first recognised reptile fossils, which was later acquired by the Teylers Museum in Haarlem. A more famous Mosasaurus fossil was found between 1770 and 1774 but was confiscated by the French in 1794 and is now in the Muséum national d'Histoire naturelle in Paris. Later dinosaur remains were discovered here as well, belonging to Betasuchus and Orthomerus, as well as turtles and fossils of smaller creatures of the sea. From 1930 through 1939 the Albert Canal was constructed, cutting through parts of Mount Saint Peter. The first ships went through in 1940. The hill's strategic location made it the site of Fort Eben-Emael (1931–35), a major artillery defence point in the Belgian defences against any invading forces coming from Nazi Germany. At the opening of the war, the entire installation was taken quickly by a relatively small number of German paratroopers. Geology and mining activities At Mount Saint Peter the rivers Geer and Meuse have cut into the limestone plateau known in the east as the Herve plateau and in the west as Hesbaye. The succeeding geologic layers include loess, gravel, quartz sand and chalky limestone of the Maastricht Formation with inclusions of flint. The chalk deposits contain numerous fossils of sea urchins, clams and belemnites. Humans have used the site since the lower Paleolithic period. The area around Spiennes is known for its flint mines. Limestone has been quarried in the area for building stone and fertilizer for many centuries. Several of Maastricht's medieval churches were built from local stone, incorrectly referred to as mergel (marl). The quarrying of limestone has created a vast network of subterranean corridors, also incorrectly referred to as grotten (caves). Although vast sections of these "caves" have now disappeared through surface mining, other sections are well-preserved. Guided tours of these limestone quarries, some with ancient inscriptions, drawings and other works of art, constitute one of Maastricht's main tourist attractions. In modern times limestone from Mount Saint Peter continues to be quarried in surface mines, mainly for portland cement production. Abandoned quarries in the Belgian part of the hill are used to dispose of ashes from municipal waste incinerators. A large quarry and cement factory operated by