Usage of base() in C#

I've been learning C# and wanted to review some open source projects to see some good written code. I found a project called Todomoo on sourceforge and there's a part that is puzzling me:

public class Category {

    // Note properties
    private int id = 0;
    private string name = "";
    private Color colour = Color.Gray;

    /// <summary>
    /// Create a new category.
    /// </summary>
    public Category() { }

    /// <summary>
    /// Load a category from the database.
    /// </summary>
    /// <param name="Id">ID of the category</param>
    public Category(int id) : base() {
        Load(id);
    }

Here it uses base() in one of the constructors, but the class is not a derived class. So what exactly is that for?

And why is the syntax of base() is that way and not like:

    public Category(int id) {
        base();
        Load(id);
    }