create dynamic div in code behind

See more:

C#

ASP.NET

bootstrap

HTML:

<div  runat="server" ID="divCategory">
  <div class="item">
    <div class="col-lg-12">
        <div class="col-sm-3">
            <img src="1.png" /><br />
        </div>
        <div class="col-sm-3">
            <img src="1.png" /><br />
       </div>
       <div class="col-sm-3">
          <img src="1.png" /><br />
       </div>
       <div class="col-sm-3">
          <img src="1.png" /><br />
       </div>
    </div>
    <div class="col-lg-12">
        <div class="col-sm-3">
            <img src="1.png" /><br />
        </div>
        <div class="col-sm-3">
            <img src="1.png" /><br />
       </div>
       <div class="col-sm-3">
          <img src="1.png" /><br />
       </div>
       <div class="col-sm-3">
          <img src="1.png" /><br />
       </div>
    </div>
  </div>
</div>

i need to write the code as above in c# code behind, this is how i get so far, can someone point out where i did wrong?

HtmlGenericControl divItem = new HtmlGenericControl("div");
  divItem.Attributes["class"] = "item";

  HtmlGenericControl divColumnH = new HtmlGenericControl("div");
  divColumnH.Attributes["class"] = "col-lg-12";

  HtmlGenericControl divColumnD = new HtmlGenericControl("div");
  divColumnD.Attributes["class"] = "col-sm-3";

  Image img = new Image();
  img.ImageUrl = "1.png";
  img.Visible = true;

  divCategory.Controls.Add(divItem);
  divItem.Controls.Add(divColumnH);
  for (int i = 0; i < 4; i++)
  {                
      divColumnH.Controls.Add(divColumnD);
      divColumnD.Controls.Add(img);
  }