August 29 is the Feast of the Martyrdom of John the Baptist.
In addition to the feast of the nativity of St. John the Baptist (June 24), the Church, since the fourth century, commemorates the martyrdom of Christ's precursor. According to the Roman Martyrology, this day marks "the second finding of his most venerable head." The body of the saint was buried in Samaria. In the year 362 pagans desecrated the grave and burned his remains. Only a small portion of his relics were able to be saved by monks and sent to St. Athanasius at Alexandria. The head of the saint is venerated at various places. That in the Church of St. Sylvester in Rome belongs to a martyr-priest John. Also in the Dominican church at Breslau the Baptist's head is honored.
Excerpted from The Church's Year of Grace, Pius Parsch
There is no doubt that blessed John suffered imprisonment and chains as a witness to our Redeemer, whose forerunner he was, and gave his life for him. His persecutor had demanded not that he should deny Christ, but only that he should keep silent about the truth. Nevertheless, he died for Christ. Does Christ not say: "I am the truth"? Therefore, because John shed his blood for the truth, he surely died for Christ.
Through his birth, preaching and baptizing, he bore witness to the coming birth, preaching and baptism of Christ, and by his own suffering he showed that Christ also would suffer.
Such was the quality and strength of the man who accepted the end of this present life by shedding his blood after the long imprisonment. He preached the freedom of heavenly peace, yet was thrown into irons by ungodly men. He was locked away in the darkness of prison, though he came bearing witness to the Light of life and deserved to be called a bright and shining lamp by that Light itself, which is Christ.
To endure temporal agonies for the sake of the truth was not a heavy burden for such men as John; rather it was easily borne and even desirable, for he knew eternal joy would be his reward.
Since death was ever near at hand, such men considered it a blessing to embrace it and thus gain the reward of eternal life by acknowledging Christ's name. Hence the apostle Paul rightly says: "You have been granted the privilege not only to believe in Christ but also to suffer for his sake." He tells us why it is Christ's gift that his chosen ones should suffer for him: "The sufferings of this present time are not worthy to be compared with the glory that is to be revealed in us."