Military men in colourful hats carry a gilded palanquin through Bangkok's old quarter in a dress rehearsal for the royal procession of Thai King Maha Vajiralongkorn's coronation -- a once-in-a-lifetime spectacle marked by pomp and ancient tradition. The royal coronation of the 66-year-old monarch will run from May 4-6 and is considered the most important event of the year in Thailand.