After a hundred years — Battle of Gettysburg

The first quatrain hints at a battlefield. The second says that many died without a proper burial. "Summer Fields" in line nine connects the battle with Abraham Lincoln via his military substitute John Summerfield Staples. After a hundred years people will "recollect" the battle through Lincoln's Gettysburg Address.

After a hundred years ¹
Nobody knows the Place
Agony that enacted there
Motionless as Peace

Weeds triumphant ranged ⁵
Strangers strolled and spelled
At the lone Orthography
Of the Elder Dead

Winds of Summer Fields ⁹
Recollect the way－
Instinct picking up the Key
Dropped by memory－

(F.1149/J.1147)

[1, 2] knows the Place:: this poem is about a place.
[3, 4] Agony, there, Peace:: a hint on a battlefield.
[5-8] Weeds, Dead:: soldiers died without proper burial due to huge lost from July 1 to 3, 1863 in Gettysburg.
[5] Weeds:: mourning clothes worn by widows. triumphant ranged:: many widows.
[6] Strangers:: those who don't know the battle. spelled:: charmed, bewitched.
[7] Orthography:: correct spelling on the grave.
[8] the Elder Dead:: soldiers died here a hundred years ago.
[9] Summer Fields:: a hint on John Summerfield Staples, a paid replacement of military service for Abraham Lincoln. This may be a satire, soldiers and politicians, death and success.
[9-10] Winds, Recollect:: Lincoln's Gettysburg speech on November 19, 1863, may let people recollect this battle. This poem was written around 1868.
[11] Key:: the major battle of the Civil War.
[12] Dropped by memory:: Dickinson assumed people will forget the battle after a hundred years.