Although I could see /http://debian-amd64.alioth.debian.org/debian-amd64 yesterday, now /http://debian-amd64.alioth.debian.org/debian-amd64 has disappeared.
Is there a trouble or is this an intentional change? /http://debian-amd64.alioth.debian.org/archive-structure.txt indicates /debian-amd64 - Structure with amd64 specific sources and arch:amd64 packages. Normal sources and arch:all packages are referenced from /debian and /debian musst reside next to this on any mirror.