In olden times the cities were surrounded with walls, designed as a defense against all enemies. The more important the city, the higher and stronger were the walls built. Having walls, it was necessary also to have gates to furnish ingress and egress to the inhabitants. These gates were in charge of faithful guardians, who had authority to open and to close them according to the regulations of the city. In accordance with this idea the city of God is represented as having "a wall great and high." This wall represents the security of Zion, whose inhabitants within can rest in peace and safety. The three gates on each side represent the free and easy access into the city from every quarter. Anciently, it was customary to give names to the gates of a city, just as we now do to our streets. The gates of this holy city were named after the twelve tribes of the children of Israel, which embraced all God's ancient covenant people, and which denotes the perfection and completeness of our heavenly home as including all the spiritual Israel. "And the wall of the city had twelve foundations, and in them the names of the twelve apostles of the Lamb." The twelve foundations, or rather the twelve courses of stone in the foundation, are more fully described hereafter. The names of the twelve tribes were on the gates to denote that the city was composed of God's true and complete Israel, and the names of the twelve apostles are on the foundation to denote that this contains the church which was "built upon the foundation of the apostles and prophets, Jesus Christ himself being the chief cornerstone." Eph. 2:20. The system of truth that they preached to the world forms the doctrinal basis of the church of God, they having received it from heaven "by inspiration of God," and their names all appear; and together they constitute one harmonious, solid foundation upon which the church shall stand forever.