If not specified, Symfony will load the application’s default module if no action is defined in the URL. The default module will show this page,

which might not be very useful to the visitors.

By default, your routing configuration file (apps/yourapp/config/routing.yml) is as the following; 

# You can find more information about this file on the symfony website:
# http://www.symfony-project.org/reference/1_4/en/10-Routing

# default rules
homepage:
  url:   /
  param: { module: default, action: index }

# generic rules
# please, remove them by adding more specific rules
default_index:
  url:   /:module
  param: { action: index }

default:
  url:   /:module/:action/*

To make it default to the module mypage for example, edit the route homepage and replace default with mypage.