Wheelbarrows as a design have been around for a long time. An early Han Dynasty wall shows Chinese labourers struggling with a load using a single free wheeling platform already not far from our present day concepts. These were used to move around weapons and people! In some, sails were used to help momentum, although it would be interesting to experiment with how stable this would be...it would be more suitable for medium distance travel than around a building site
In Ancient Greece they were used to move building materials. Medieval Europe saw the first ones in around the year 1200 although mainly in the lowlands. While they remain primarily the same design every now and again something revolutionary occurs. These include the introduction of a ball rather than a wheel in the 1970's by James Dyson and some powered varieties. As the majority remained pushed maybe the iTip will be the next revolution in the ancient wheelbarrow's evolution.