session的问题

我做了一个切换城市的用户控件，默认的城市是北京，当我点选中其他的城市时，首页的城市就会变成我选中的那个城市，可其他页面还是北京阿？
代码如下：
CS代码：
protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            Session["city"] = Literal_City.Text;
        }
        
    }
    protected void bj_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "北京";
        Session.Add("city", Literal_City.Text);
    }
    protected void tj_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "天津";
        Session.Add("city", Literal_City.Text);
    }
    protected void sh_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "上海";
        Session.Add("city", Literal_City.Text);
    }
    protected void cq_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "重庆";
        Session.Add("city", Literal_City.Text);
    }
    protected void xa_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "西安";
        Session.Add("city", Literal_City.Text);
    }
    protected void sjz_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "石家庄";
        Session.Add("city", Literal_City.Text);
    }
    protected void ty_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "太原";
        Session.Add("city", Literal_City.Text);
    }
    protected void sy_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "沈阳";
        Session.Add("city", Literal_City.Text);
    }
    protected void cc_Click(object sender, EventArgs e)
    {
        Literal_City.Text = "长春";
        Session.Add("city", Literal_City.Text);
    }

html代码：
<div style="width:357px; float:left; line-height:46px; height: 195px;">
世纪新网 >> 生活分类信息:<span class="hong25"><asp:Literal ID="Literal_City" runat="server" Text="北京"></asp:Literal></span>|<span  onmouseover="city.style.display = 'block'" onmouseout="city.style.display='none'">[<a href="#">切换城市</a>]</span>
    <div id="city" onmouseout="this.style.display='none'" onmouseover="this.style.display='block'" style="left: 254px; top: 28px">
        &nbsp;<asp:LinkButton ID="bj" runat="server" OnClick="bj_Click" >[北京]</asp:LinkButton>
    <asp:LinkButton ID="tj" runat="server" OnClick="tj_Click" >[天津]</asp:LinkButton>  
    <asp:LinkButton ID="sh" runat="server" OnClick="sh_Click" >[上海]</asp:LinkButton>
    <asp:LinkButton ID="cq" runat="server" OnClick="cq_Click" >[重庆]</asp:LinkButton>
    <asp:LinkButton ID="xa" runat="server" OnClick="xa_Click" >[西安]</asp:LinkButton>
    <asp:LinkButton ID="sjz" runat="server" OnClick="sjz_Click" >[石家庄]</asp:LinkButton>
    <asp:LinkButton ID="ty" runat="server" OnClick="ty_Click" >[太原]</asp:LinkButton>
    <asp:LinkButton ID="sy" runat="server" OnClick="sy_Click" >[沈阳]</asp:LinkButton>
    <asp:LinkButton ID="cc" runat="server" OnClick="cc_Click" >[长春]</asp:LinkButton>
</div></div>


大家帮忙解决一下阿！！！谢谢了！！！