Sardis in the Bible

Revelation 1:11 Saying, I am Alpha and Omega, the first and the last: and, What thou seest, write in a book, and send it unto the seven churches which are in Asia; unto Ephesus, and unto Smyrna, and unto Pergamos, and unto Thyatira, and unto Sardis, and unto Philadelphia, and unto Laodicea.
Revelation 3:1-4 And unto the angel of the church in Sardis write; These things saith he that hath the seven Spirits of God, and the seven stars; I know thy works, that thou hast a name that thou livest, and art dead. 2 Be watchful, and strengthen the things which remain, that are ready to die: for I have not found thy works perfect before God. 3 Remember therefore how thou hast received and heard, and hold fast, and repent. If therefore thou shalt not watch, I will come on thee as a thief, and thou shalt not know what hour I will come upon thee. 4 Thou hast a few names even in Sardis which have not defiled their garments; and they shall walk with me in white: for they are worthy.