The post was expanded again in 1871-1872 with the arrival of Colonel William B. Hazen's 6th Infantry Regiment to a six-company infantry post covering approximately a square mile, including laundress' quarters and other civilian areas, using lumber shipped from the Eastern United States by steamboat but with no stockade. At that time the fighting had moved further westward into Montana Territory and the garrison was large enough to no-longer need the perimeter stockade. The original Commanding Officer's Quarters at the site today was part of this expansion and originally built in 1871-1872 and served as Hazen's residence from 1872-1880. This structure sits at the southern end of what once was a double row of Officer's Quarters that ran towards the North. Beyond this double row the stone Powder Magazine was built in 1875 out of sandstone quarried from an area located to the North of the fort. When in use the magazine held over a million rounds of ammunition for the fort's garrison, much of it being black powder cartridges one of which was the .45-70. At this time Fort Buford became a key element in the supply route for the military campaigns of 1876-1877 in Montana Territory. At the peak of occupation, which followed the Battle of the Little Bighorn in 1876 until 1881, there were just under 100 buildings and approximately 1,000 people occupying the post at any given moment including infantry and cavalry companies bivouacking in tents on the parade ground while being resupplied.