How to overload a matrix class?

[featips]

Suppose I define a class called Matrix

template <class T>
class Matrix {
    ......
private:
    vector< vector<T> > data;
};

My question is: how to overload Matrix[i][j] which take two integers i and j as parameters?

This is an interview question that I was asked, and the interviewer precluded the way of using Matrix(i,j). Thanks a lot.