Add width, height and frameborder in your iframe as shown below
width='100%' height='700' frameborder='0'
Try this, i think now it's works
<iframe src='embed.verite.co/timeline/?source=0Aj2TitNEGaD2dHlqV3ZRcDhMYlY3MjZmUEt2aWQ0ckE&font=Bevan-PotanoSans&maptype=toner&lang=en' width='100%' height='100%' frameborder='0'></iframe>