"De Rerum Natura"
Lucretius was a Roman poet, who set himself the task of writing with great clarity that this is a material universe which we call Nature, and there is nothing “outside” of nature.
The version by Rolfe Humphries translation into English is a well-respected translation into English.
You can also make your way book by book with the Lucretius Today Podcast. This is an amazing (free) resource for understanding the implications of the poem and its content.
You can read more about it on Wikipedia.