When were concrete blocks invented?

[chuckey]

Just taken down a dry stone garden wall in a stone built Yorkshire cottage (dated circa 1805). The wall has obviously be re-built at some time and I am curious to know when.
Frank

 

[LadyArowana]

Internet says this http://www.ehow.com/about_4674117_were-concrete-blocks-first-made.html must be true :lol: