Set bottom gravity to a single view Android

I have a horizontal linear layout, with 3 buttons, on the display. I want this layout to be displayed in the bottom of the display.

Here is the code I wrote:

<RelativeLayout xmlns:android="http://ift.tt/nIICcg"
    xmlns:tools="http://ift.tt/LrGmb4" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context="flowepower.tetris.Game"
    android:background="@drawable/Main_screen">
    <LinearLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="bottom"
        android:orientation="horizontal" 
       </LinearLayout> </RelativeLayout>

I haven't put the buttons code, they are simple ones.

With this code, it is still displayed on the top. Can you suggest me other posibilities? Thank you!