Why does PHP use \ instead of / for namespaces?

e.g.

  namespace Foo\Bar\subnamespace;

instead of:

  namespace Foo/Bar/subnamespace;

it seems like, in 2008/9, when the decision was being made/implemented, the arguments were around whether or not to stick with the '::' operator or find some new symbol.

as a much more casual coder, i find the backslash operator annoying.

and it's the type of aesthetic thing that bothers me more than other things that seem to bother other folks much more -- alleged less than ideal type coercion, etc.

i'm assuming using the forward slash, '/', was just a non-starter, but....was it?