As you know, in classical literature the dead are referred to as shades, but here in Milton's simile "shades" merely means "shade trees."

在古典文学里，逝者常被用树荫来指代，而在这里弥尔顿的比喻“树荫“仅表示“叶绿成荫的树“

耶鲁公开课 - 弥尔顿课程节选

This is the initial part of the simile that describes the leaves: "thick as Autumnal Leaves that strow the Brooks / in Vallombrosa, where th' Etrurian shades / high overarch't imbow'r."

这是描写落叶的比喻的开始部分：,“他们人数众多，稠密得像秋天的繁叶,/在瓦隆布罗萨，厄特鲁利亚的光辉逐渐暗淡“

耶鲁公开课 - 弥尔顿课程节选