The stone placed in the center of the top tier of the circular mound altar 天心石即圜丘坛上层坛面的中心石。
2.
The main buildings on a central axis from top to bottom : hall of prayer for good harvest , imperial vault of heaven and circular mound altar 天坛主要建筑物集中在内坛中轴线,由上至下分别为祈年殿皇穹宇和圜丘坛。
3.
Also known as heaven mound altar , it is five meters high and of three tiers . around each tier there are white marble balusters 圜丘坛俗称祭天台,是一座由汉白玉石雕栏围绕的三层石造圆台,通高5米余,洁白如玉,极为壮观。