Paradox Interactive announces April 5th is when to expect the release of Mare Nostrum, the upcoming naval-themed expansion for Europa Universalis IV, their historical strategy game. A new video developer diary features Johan Andersson explaining some of the new features in the expansion, showing off some gameplay, and also revealing some significant changes in a free patch for all users that will accompany the add-on. Here's word:

Mare Nostrum adds new depth to many parts of the classic empire builder, including new options for the merchant republics. These tiny financially motivated states can now form Trade Leagues, uniting their commercial might in a military and a mercantile alliance that makes everyone richer and stronger.

The expansion also introduces new mercenary options with greater control over your naval missions, the chance to rent your armies as condottieri, and the ability to share maps with your neighbors.

A new developer video with Creative Director Johan Andersson outlines some of the coming changes.

And, even if you pass on buying Mare Nostrum, April 5 will also be the occasion for a substantial free update for all Europa Universalis players. This massive patch will add new features, which will enhance the player experience. The update will include:

• Map Expansion: Greater detail to Ireland and sub-Saharan African, especially in the Congo and East Central Africa, and new “States and Territories” system
• Espionage Reworking: Your diplomats can now build spy networks in enemy nations, from where you can fabricate claims on enemy holdings or undermine them from within.
• Interface improvements: Better tooltips overall, and naval blockades are now more obvious on the map
• Naval Combat Changes: better morale system and increased chance to capture enemy vessels
• And even more changes to game balance, AI and modding triggers