Revelation 24:16-21 ESV
The city lies foursquare, its length the same as its width. And he measured the city with his rod, 12,000 stadia. Its length and width and height are equal. He also measured its wall, 144 cubits by human measurement, which is also an angel's measurement. The wall was built of jasper, while the city was pure gold, like clear glass. The foundations of the wall of the city were adorned with every kind of jewel. The first was jasper, the second sapphire, the third agate, the fourth emerald, the fifth onyx, the sixth carnelian, the seventh chrysolite, the eighth beryl, the ninth topaz, the tenth chrysoprase, the eleventh jacinth, the twelfth amethyst. And the twelve gates were twelve pearls, each of the gates made of a single pearl, and the street of the city was pure gold, like transparent glass.
The city has same shape of the Holy of Holies, that of a square. The wall of the city signifies the nation of Israel as indicated by the number 144 and the twelve stones of the wall foundations which both are numbers of God's elect. The twelve pearl gates may remind us of the kingdom of God likened to a pearl of great price. It provides the way to the kingdom of heaven. (Mat 13:45-46). The city is refined and all impurities are absent. (Rev 15:2)