Having been heavily exploited in Roman times, the iron ore in the Wealden rocks took on great importance when blast furnaces were introduced from the continent in the 1490s. Within a century a thriving industry was established in Sussex. The Myllwood Furnace, as it was called, was operated by John Thorpe, who lived at Gibbshaven, and worked in conjunction with the Woodcock Hammer (now the Wiremill, near Felbridge). The furnace seems to have closed down early in the 17th century.
During the 1600s some small parcels of land began to be enclosed around the edge of Crawley Down. One or two more farms had been established in the previous century, such as Down Park Farm (then called Shepherds Hole) and Burleigh Cottage (then Sandhill Gate), both on the edge of the common. But the character of the area had not changed. Similarly, on Snowhill, to the north of Crawley Down, at that time part of Copthorne Common, enclosures had been taking place reflecting a rise in the number of smallholders. This continued into the next century when an important change took place. The old farm of Clarke‘s was demolished in the mid 1700‘s and replaced by the Grange; probably built for Joseph Wright, a London silversmith, it was the first substantial mansion built in the area for 200 years and an indication of the pattern of growth in the ensuing century.
Following a change in the ownership of the Manor of Hedgecourt whereby the Gage family sold to the Evelyns, what became known as the Warren Furnace began operations again, this time in the charge of Edward Raby, a London ironmonger. He probably leased the furnace in about 1758 to take advantage of the profits to be made supplying guns to the Board of Ordnance during the war then being waged against the French. The loss of contracts at the end of hostilities may have contributed to his bankruptcy, but Raby soon recovered, leased Gravetye furnace and, as well as working in iron, the traditional material of the Weald, expanded into casting bronze guns. However, the furnace, like the others in Sussex, succumbed to the more efficient competition of the Midland and Scottish founders and closed down in 1774.
The wild and remote nature of Crawley Down, and its closeness to London, briefly made it a popular venue for the illegal sport of prizefighting in the first quarter of the 19th century, with huge and boisterous crowds gathering to watch the bouts. But more civilising influences were at work.