August 29 is the Feast of the Martyrdom of St. 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