Can lists be defined in a special way so that they contain things of different type?

In it is written that

A type $ \tau$ list is the type of lists with elements of type $ \tau$

Why must a list contain elements of the same type? Why can’t it contain elements of different types?

Is there a way of defining a list polymorphically in the typed lambda calculus, so that it takes elements of any type?

Can we then use the List monad on lists, defined polymorphically?