A lot of work.
To keep out KONG!
Very much so. It's surprising how many times that got done, by hand (or perhaps with the help of beasts of burden), here and there. Corliss reproduces a map of western England/eastern Wales to show the route of Offa's Dyke, which is attributed to Offa of Mercia. There's an earlier, apparently much shorter work called Wat's Dyke that antedates Offa's; there's also the post-Roman Wansdyke, which runs west to east across a good bit of southern England, and a very short (probably unfinished) earth barrier called Devil's Dyke, also post-Roman. Ooh, I just took another look at the map, and it doesn't show Offa's Dyke, but that's what's discussed above it.