In message , Matthew
Church writes

Something else that has bothered me recently. London's first (proper)
railway The London and Greenwich was built *entirely* on a viaduct to
prevent collisions with cattle!?

I don't think so. It was on viaduct because it crossed more than 30
roads, and that number of level crossings on so short a line would have
presented enormous operational difficulties. In particular, the first
mile or so out of London Bridge was already very densely built-up by the
1830s.

--
Paul Terry