1914 - Caratheodory showed how to compute length in any dimension, and (more generally) p-dimensional measure in q-dimensional space for integers p ≤ q.

1918 - Hausdorff observed that Caratheodory's construction works - and is interesting - even when p is not an integer.

1929 & later - Besicovitch developed the Hausdorff measure into a powerful mathematical tool.