You can insert a horizontal rule across the page by typing four or more dashes. The number of dashes in a horizontal rule markup determines how thick it is, up to a limit of 10.

For more information on the possible markup, see HelpOnEditing.

--- (not a rule)
----
-----
------
-------
--------
---------
----------
-------------------------------------------- (not thicker than 10)

--- (not a rule)

-------------------------------------------- (not thicker than 10)