The Basic Moat increases the overall castle defense. It is effective for both melee & ranged defenders. First two levels can be built with wood & stone, while the 3rd level requires "Construction" & "upgrade" tokens which will give you +25% of protection. You may further increase your moat protection with upgrading also the "Castle moat" (which can be purchased with rubies and can give up to +40% protection). To further increase your defense you should use moat tools when you set up your castle defense formation.