Content delivery networks (CDNs) deliver content objects for others is disclosed. End user computers are directed to an edge server for delivery of a requested content object by a universal resource indicator (URI). When an edge server does not have a copy of the content object from the URI, information is successively passed to ancestor servers within a hierarchy until the content object is found. There can be different hierarchies designated for different URIs or times at which requests are received. Once the content object is located in the hierarchical chain, the content object is passed back down the chain to the edge server for delivery.