Sri Rudram is the only long hymn, consisting of hundreds of namas, that occur in the Vedas. Other common major hymns are from Itihasas, eg., Vishnu Sahasranamam from Mahabaratha, or, from Puranas, e.g., Lalitha Sahasranamam from Brahmanda Puranam. In content and format, there are lot of similarities between Sri Rudram and the other hymns like Vishnu Sahasranamam.