1, also referred to as the “root site”, is the first site in a multisite network and will be listed first in the Network Admin > Sites dashboard.
The root site should be used for administrative purposes only: with a default theme activated, no content added to it, and access to the site restricted by Maintenance Mode.
All new subsites added to a multisite network will initially exist as subdirectories of the root site’s domain. It can therefore be useful to have a custom domain in subsite
1 for branding purposes, such as