Note, written on the back of a plan which accompanied the group of architectural drawings for Purfleet Magazine. The note contains specifications of some of the wharfing to be executed at Purfleet. The gunpowder magazine was built in the 1760s to replace a magazine in Woolwich which had been damaged in an explosion. Purfleet had five large magazine buildings used to store gunpowder and each could accommodate 10,400 barrels. Water mills had stood here on the Marr Ditch (now known as the Mardyke) but these had the effect of letting salt water from the river seep into the land. This was thought to be detrimental to the land and so the mills were taken down and new sluices were built as a more efficient drainage system. Wooden floodgates were built to protect the fort from the danger of flooding from the River Thames.