The Tang dynasty reached its peak during Emperor Xuanzong's reign.
Tips
usage
全盛 almost always pairs with 时期 ('period') or 时代 ('era') - 全盛时期 is a fixed collocation meaning 'heyday' or 'golden age'. Used for empires, careers, athletes, art movements.
memory
全 = 'whole/full' + 盛 = 'flourishing/abundant' -> 'fully flourishing'. Think of a tree in full bloom with every branch covered.
