Why is Crimea so important to both Russia and Ukraine?

The Russian naval headquarters in Sevastopol is one of Moscow's most important bases. https://www.aljazeera.com/program/inside-story/2023/9/24/why-is-crimea-so-important-to-both-russia-and-ukraine?traffic_source=rss&feed_id=8886&_unique_id=6510d27fc94c6