On the margins of London, on the edge of Rainham Marshes, and on the banks of the Thames, is the Essex town of Purfleet. Its residents are probably right to feel somewhat overlooked (they hope a name change to Purfleet-on-Thames will help): chances are that you haven't visited, unless you are a birdwatcher or have business at the Freight Terminal. I was certainly unaware of the surprisingly significant Purfleet Magazine until I happened across it while on a visit to somewhere else. 
Until alternatives developed in the late nineteenth century, the British military was dependent upon gunpowder. However, storing the substance was fraught with danger: contact with a spark could lead to explosions. It was therefore stored in wooden barrels, themselves kept in solid buildings, hedged with precautions. Some of the sites were surprisingly central - such as the Tower of London and Hyde Park - since they needed to be available for use. However, larger supplies were kept in more remote locations. Thus in 1760, an Act of Parliament established the Royal Gunpowder Magazine at Purfleet to replace one on Greenwich Peninsula. It was the main storage center for gunpowder.
By 1773, five magazines had been built, each able to hold over 10,000 barrels of gunpowder. Their roof voids were filled with sand, the walls were brick with few window openings. Copper panels helped to reflect some light into the interiors. Powder was delivered from mills, notably Waltham Abbey Royal Gunpowder Mills, and tested in the proof house on arrival. It was then stored until needed by the army or navy. A garrison of soldiers kept the magazines, enclosed within high security walls, secure; the civilian workers inside wore safety clothes and were bound by strict rules including a prohibition on smoking.
In 1962, the site was closed and some of the buildings demolished. Magazine No. 5 and the proof house do survive, tangible evidence of Purfleet's past importance. Indeed, the magazine is now a heritage center - closed during my brief visit, but somewhere I plan to return.
