Ipad Mini, Safari, Show All Windows

How do you delete all the opened website in Safari? When I go to the main page and press the Safari icon for two seconds, a small pop-up appears giving me some options such as Edit Home Screen, Show All Windows, Show Reading List, etc. When I choose Show All Windows, I see about 17-18 screens of Safari windows are open. How do I get rid of them? Even if I delete the history of the web browser in Safari, they do not disappear from Show All Windows screen.

Thank you.