How do I avoid specifying arguments for a class template that has default template arguments?

If I am allowed to do the following:

template <typename T = int>
class Foo{
};

why am I not allowed to do the following in a place like main:

Foo me;

but must instead specify the following?

Foo<int> me;

C++11 introduced default template arguments, and, right now, I'm finding them difficult to fully understand.