Before the mid-1860s, farmers had to build fences from materials that were readily available or grown on the farm. Then lightweight fencing wire became available, and about 6 million hectares of farmland were fenced over the next 20 years – mainly on flat land. The next major boom in fencing was not until the 1950s, with the advent of aerial topdressing and the use of aircraft to transport fencing materials onto hill country.