Is the category of sheaves on a site a 1-category or a 2-category?

Question

In the use of the term topos I read about today, $\mathfrak{Top}$ is a 2-category. In the first use I ever read about a topos was just a category of sheaves on a site. I didn't think if it was a 2-category instead of a 1-category though. Is the category of sheaves on a site a 1-category or a 2-category?