Pieter Arnoldus Cronjé, commonly known as Piet Cronjé ('KRON-year') (Colesberg, Cape Colony, 4 October 1836 – Potchefstroom, Transvaal, 4 February 1911) was a general of the South African Republic's military forces during the Anglo-Boer wars of 1880-1881 and 1899-1902.
Born in the Cape Colony but raised in Transvaal, Cronjé made his reputation in the First Boer War, besieging the British garrison at Potchefstroom. He had a distinctive appearance, being short with a black beard and was reputed to have considerable personal courage.
He was in command of the force that rounded up Jameson at Doornkop at the conclusion of the Jameson Raid on 2 January 1896. During the Second Boer War Cronjé was general commanding in the western theatre of war. He began the sieges of Kimberley and Mafeking. At Mafeking, with a force varying between 2,000 and 6,000 he laid siege against 1,200 regular troops and militia under the command of Colonel Robert Baden-Powell.
His novel tactics at the Battle of Modder River, where his infantry were positioned at the base of the hills instead of on them (in order to increase the effectiveness of their rifles' flat trajectories) earned him a place in military history.
After his surrender with 4,000 of his commandos at Paardeberg on 27 February 1900, he was imprisoned as a prisoner of war in St. Helena Island where he remained until the conclusion of peace negotiations in 1902.