pomerium

Pomerium is a Latin term meaning boundary, most notably referring to the sacred boundary around an ancient Roman city. It denotes the space within which the city’s civil and religious activities were governed by Roman law and ritual, and outside of which the gods and foreign powers were believed to hold sway.

In Rome, the pomerium signified the religious and legal limits of the city. Weapons were traditionally prohibited within the boundary, and the authority of magistrates was defined in relation to this sacred line. The boundary could be expanded by ritual acts connected with urban growth or the dedication of new temples, and the phrase within the pomerium carried ceremonial and legal significance in historical sources.

Pomerium is also the name of an open-source software project that functions as an identity-aware access proxy for securing internal applications. It sits as a reverse proxy between users and services, enforcing access policies based on identity provided by authentication systems such as OpenID Connect, OAuth2, SAML, or mTLS certificates. Pomerium enables zero-trust style access to internal endpoints by allowing administrators to define policy rules that determine who may access which services. It can protect applications deployed on-premises or in cloud environments and is commonly run in containerized environments, including Kubernetes, to provide centralized authentication, authorization, and access control for web services and APIs.