COEHORN, MENNON, BARON DE, a celebrated Dutch engineer, who was born in 1632. Ile commenced his military career at an early age, and spent the leisure which the Intervals of active duty afforded in improving the art of fortifying places, with the view of diminishing the ieseqnaLty which, by the inventions of his contemporsy Vauban, began then to be felt in the means of attack and defence. The services which Coehorn rendered to his country, both as an engineer and a commander, at a time when the defence of its military poets was an object of the first importance, procured for him the most houourable appointments which a soldier can attain. Ile arrived at the rank of general of artillery, and was made director-general of fortifications and governor of Flanders.
At the siege of Namur In 1602, Coehorn gallantly defended the fort which he had before constructed for the purpose of strengthening the citadel of that place; but being dangerously wounded he was at length compelled to surrender. Vauban, who conducted the operations of the attack on this occasion, rendered full justice to the talents and valour of his rival.
Coehorn was engaged at the attack of Trarbach, Limburg, Liege, and at that of the citadel of Namur, which three years before he had defended. In the year 1703 he was employed at the siege of Bonn,
where, in three days, his heavy and well-directed cannonade caused the surrender of the place. Soon afterwards he forced the French lines at Ilimuye, and was appointed with his army to keep in check the Marquis de Lledmar on the right bank of the Scheldt. This was his last service; in the following year (1701) be died at the Hague, at the age of seventy-two.
In 1655 Coehorn published what are called his 'Three Systems of Fortificatimi ;' they are adapted to ground elevated but from three to five feet above the surface of water, and consequently they may be considered as applicable only to the towns of Holland. He was appointed to repair or reconstruct the fortifications of Nitnegucn, Breda, Mannheim (since destroyed), and Bergen-op-Zoom. The siege of the last place in 1747, by its duration and the lessee which the besiegers sustained in its progress, attests the merit of the system ou which the works were constructed.