为什么我的翻译矩阵需要转置?

I'm working on a small graphics engine using OpenGL and I'm having some issues with my translation matrix. I'm using OpenGL 3.3, GLSL and C++. The situation is this: I have defined a small cube which I want to render on screen. The cube uses it's own coordinate system, so I created a model matrix to be able to transform the cube. To make it myself a bit easier I started out with just a translation matrix as the cube's model matrix and after a bit of coding I've managed to make everything work and the cube appears on the screen. Nothing all to special, but there is one thing about my translation matrix that I find a bit odd.

现在据我所知，一个平移矩阵的定义如下:

1, 0, 0, x
0, 1, 0, y
0, 0, 1, z
0, 0, 0, 1

1, 0, 0, 0
0, 1, 0, 0
0, 0, 1, 0
x, y, z, 1

//this is called just before cube is being rendered
void DisplayObject::updateMatrices()
{
    modelMatrix = identityMatrix();
    modelMatrix = modelMatrix * translateMatrix( xPos, yPos, zPos );

    /* update modelview-projection matrix */
    mvpMatrix = modelMatrix * (*projMatrix);
}

//this creates my translation matrix which causes the cube to disappear
const Matrix4 translateMatrix( float x, float y, float z )
{
    Matrix4 tranMatrix = identityMatrix();

    tranMatrix.data[3]  = x;
    tranMatrix.data[7]  = y;
    tranMatrix.data[11] = z;

    return Matrix4(tranMatrix);
}

#version 150 core

in vec3 vPos;

uniform mat4 mvpMatrix;

void main()
{
    gl_Position = mvpMatrix * vec4(vPos, 1.0);
}

void DisplayObject::render()
{
    updateMatrices();

    glBindVertexArray(vaoID);
    glUseProgram(progID);
    glUniformMatrix4fv( glGetUniformLocation(progID, "mvpMatrix"), 1, GL_FALSE, &mvpMatrix.data[0] );
    glDrawElements(GL_TRIANGLES, bufferSize[index], GL_UNSIGNED_INT, 0);
}

1, 0, 0, 0
0, 1, 0, 0
0, 0, 1, 0
x, y, z, 1