Synagogues may be considered "oldest" based on different criteria, and can be oldest in the sense of oldest surviving building, or oldest in the sense of oldest congregation. Some old synagogue buildings have been in continuous use as synagogues, while others have been converted to other purposes, and others, such as the Touro Synagogue, were shuttered for many decades. Some early established congregations have been in continuous existence, while other early congregations have ceased to exist.