I'm trying to learn Silex/Twig, but I've come across a small issue... In every "tutorial" I've seen, the speaker uses the "asset"-function to include JS and CSS. Unfortunately, this doesn't seem to work for me...

Code PHP:
<link href="{{ asset('/css/index.css') }}" rel="stylesheet" media="all" />
I get the following error: "Twig_Error_Syntax: The function "asset" does not exist in "base.html" at line 8"

I can replace the css-include to the following and it works:
Code PHP:
<link href="{{ app.request.basepath }}/css/mails.css" rel="stylesheet" media="all" />

I'm just wondering why the first piece of code isn't working...


Edit: I downloaded Silex fully on their site (.zip)