Just after midnight on June 21, 2000, Midsummer Day, artist Andy Goldsworthy supervised the unloading of 13 huge snowballs from refrigerated trucks onto the streets of London. What took place as an astonished public came upon these snowballs - each weighing about a ton - is captured in spontaneous and evocative pictures taken by photographers working around the clock. Here, then, is the story of Goldsworthy's largest ephemeral work to date. Made in one century (the 20th) and unwrapped to melt very slowly in the next, this is four-dimensional sculpture in which the lifespan and history of the snowballs are as important as their appearance at any moment. As Judith Collins explains in her introduction, and Goldsworthy in his diaries, this is a natural progression from his previous work with snow. Goldsworthy presents a unique confrontation between the wilderness and the city - snowballs made in the Scottish winter brought to the streets of London in the summertime.

Judith Collins is former senior curator of British art, Tate Gallery, London.