This paper presents a comprehensive experimental study on the use and impact of external repositories in the Maven ecosystem. For this research the prevalence, naming patterns, and potential risks associated with external repositories were analyzed. We analyzed 199,188 packages and found that 3.29% of projects employ external repositories. Our findings indicate a decline in the usage of external repositories over time, with one (1.85%) and two (0.72%) external repositories occurring the most. The usage of external repositories has no significant (p < 0.05) effect on the error rate. However, 19.85% of the errors of packages that use an
external repository are caused by one of their external repositories. Moreover, we found that 69.58% of the repository urls were unreachable. 19.31% of the unique ids have two or more different repository urls associated with them. Based on our findings, developers are urged to thoroughly evaluate their usage of external repositories and to consider checking their settings.xml and POM.xml files to
ensure no url or id collisions are prevent or causing unintended behaviour.