Board Thread:General Discussion and Questions/@comment-28424239-20160522000351/@comment-27904998-20160522070747

You need to complete five artifact collections. They are similar to regular collections, except you need to complete a set of collections before an artifact becomes available. Once you've completed an artifact, you'll get a symbol under the artifact award like this:

It doesn't matter which artifacts you complete, you just need to complete five of them.