ARM architectures not available for Ubuntu 18.04

Hello, I'm currently trying to build a package on Ubuntu 18.04 with x86 and ARM architectures (aarch64 and armv7l) enabled. The x86 builds work fine, but the ARM builds fail to start as "unresolvable" because none of the packages are available ("nothing provides <package>".) Are the ARM architectures not enabled on 18.04? I thought I'd heard that they were. Kyle