We welcome to Barcelona the biggest cruise ship ever built, Royal Caribbean's Symphony of the Seas. Taking the occasion, we have elaborated a list of vessels that have excelled in its category. MS Symphony of the Seas is an Oasis-class cruise ship owned and operated by Royal Caribbean International. As of 9 June 2017, she is the largest passenger ship ever to be constructed by gross tonnage, at 228,021 GT, surpassing her sister Harmony of the Seas.