there is a story of a pig falling into the Fleet ditch in the seventeenth century. (The Fleet is one of London's 'lost' rivers). It was found a week or so later --alive - and much heavier .....and correspondingly more valuable.......
well, I guess we can imagine the sort of things it was eating - so there you have it - the Avebury ditch was a big pig trough for fattening up the skinny ones