Henri Alexis Brialmont (May 25, 1821 - June 21, 1903) was a Belgian military engineer. He was one of the leading fortifications engineers in the 19th century.

He was son of General Laurent Mathieu Brialmont (d. 1885) and was born at Venloin Limburgon. Brialmont was educated at the Brussels military school, he entered the army as sub-lieutenant of engineers in 1843, and became lieutenant in 1847. From 1847 to 1850 he was private secretary to the war minister, General Baron Chazal. In 1855 he entered the staff corps, became major in 1861, lieutenant-colonel 1864, colonel in 1868 and major-general in 1874. In this rank he held at first the position of director of fortifications in the Antwerp district (December 1874), and nine months later he became inspector-general of fortifications and of the corps of engineers.

In 1877 he became lieutenant-general. His far-reaching schemes for the fortification of the Belgian places met with no little opposition, and Brialmont seems to have felt much disappointment in this. At any rate he went in 1883 to Romania to advise as to the fortification works required for the defence of the country, and presided over the elaboration of the scheme by which Bucharest was to be made a first-class fortress. He was thereupon placed en disponibilite in his own service. His services were, however, too valuable to be lost, and on his return to Belgium in 1884 he resumed his command of the Antwerp military district. He had, further, while in eastern Europe, prepared at the request of the Hellenic government, a scheme for the defence of Greece. He retired in 1886, but continued to supervise the Romanian defences.

In the first stage of his career as an engineer Brialmonts plans followed with but slight modification the ideas of Vauban; and his original scheme for fortifying Antwerp provided for both enceinte and forts being on a bastioned trace . But in 1859, when the great entrenched camp at Antwerp was finally taken in hand, he had already gone over to the school of polygonal fortification and the ideas of Montalembert. About twenty years later Brialmonts own types and plans began to stand out amidst the general confusion of ideas on fortification which naturally resulted from the introduction of long-range guns, and from the events of 1870/1871.

The extreme detached forts of the Antwerp region and the fortifications on the Meuse at Liege and Namur were constructed in accordance with Brialmonts final principles, viz, the lavish use of armour to protect the artillery inside the forts, the suppression of all artillery positions open to overhead fire, and the multiplication of intermediate batteries. In his capacity of inspector-general Brialmont drafted and carried out the whole scheme for the defences of Belgium. He was an indefatigable writer, and produced, besides essays, reviews and other papers in the journals, twenty-three important works and forty-nine pamphlets. In 1850 he originated the Journal de l'armee Beige .

His most important publications were:

• La Fortification du temps present (Brussels, 1885)
• Influence du tir plongeant et des obus-torpilles sur la fortification (Brussels, 1888)
• Les Regions fortifiees (Brussels, 1890)
• La Defense des 'tats et la fortification a la fin du XIXe siecle (Brussels, 1895)
• Progres de la defense des etats et de la fortification permanente depuis Vauban (Brussels, 1898).