The first ‘manholes’ are from the Roman era when they were slabs of stone or wood to enable easier access over stone-covered channels carrying water or sewage.
The style of manholes we are familiar with today – mostly a removable cast-iron cover, round or rectangular and at least the width of a worker’s shoulders, concealing an underground shaft – are evidence of the rapid development of utility services and infrastructure in Victorian and Edwardian Britain. More here .
Japan meanwhile is renowned for its highly colourful manhole covers, two of which are shown below.
A couple of bits of info you might not know. Most manhole covers are round so the covers can never accidentally fall inside.
Jeremey Corbyn (ex Labour Party leader) is a big fan and collects manhole covers!