The clacks in Terry Pratchett's Discworld novels is a network of semaphore towers stretching along the Sto Plains, into the Ramtops and across the Unnamed Continent to Genua. It was introduced in The Fifth Elephant and has become the Discworld's first network telecommunications network. While the system structure is that of a telegraph, elements of it are often described as similar to the Internet; for example, it threatens to make the Post Office obsolete in Going Postal (which also features a group of clacks hackers) and is sometimes described as 'c-mail' (a clear reference to email). 'C-commerce' is also carried out on it.