Robert N. Miller was the son of Robert Miller, who became a wealthy plantation owner in Raymond, Mississippi before the Civil War. Robert Miller in turn was the son of Joseph Miller (brother of Ebenezer, Erskine’s father) and Margaret Reid (the sister of Margery Reid, wife of Ebenezer). Thus Erskine Miller and Robert Miller were double first cousins. Robert N. Miller was a District Attorney and later defense lawyer who were known as one of the best criminal defense lawyers in Mississippi.

Graduate of the University of Mississippi, class of 1869

I suspect he may have served with Ashcraft's Battalion Cavalry
http://www.mississippiscv.org/MS_Units/3rd_Bn_MS_St_Cav.htm

These are all the Robert Millers I found in Mississippi rosters, there were no Robert N's

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Robert Miller, Private, Company B, 3rd Battalion (Ashcraft's) Mississippi Cavalry, enlisted January 23, 1864 at Chesterville, Miss. for 2 years, absent on Special Service May 5, 1864,
17 year old Farmer, 5' 5", born in Miss., blue eyes, light hair, fair complexion, no other records

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Robert Miller, Private, Capt. E. W. Lacey's Company of Drafted Militia, Mississippi State Troops,* drafted August 4, 1862 at Columbus, Miss. by J. V. Harris for an indefinite period, recorded absent on sick leave February 28, 1863, mustered out of service at Columbus, Miss. September 22, 1863, no further records

* This company subsequently became Company D, 3rd Battalion Mississippi [Minute Men] Infantry (State Troops)

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Robert Miller, Palo Alto Guards (Geo. H. Moore, Capt.), appears on a list of the Palo Alto Guards, a company organized at Palo Alto, Miss. for home defense under act of Congress No. 28, approved Oct.__,1862; each member to furnish his own arms, ammunition, horse, equipment, etc., no date, no other records

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Robert Miller, age 27, Private, Capt. Alfred Hudson's Company (Pettus Flying Artillery), Mississippi Volunteers,** joined for duty and enrolled May 11, 1861 at Panola, Miss. by Wm. H. Brown for 12 months, discharged on Medical Certificate June 15, 1862 at Tupelo, Miss.

** This company subsequently became Capt. Hoole's Company, (The Hudson Battery), Mississippi Light Artillery

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Robert Miller, age 42, Private, Capt. T. C. Lipscomb's Company, Harrison's Regiment of Cavalry,*** enlisted September 7, 1863 at Columbus, Miss. by Capt. Lipscomb for the war, paroled May, 1865, resident of Lowndis County, Ky.

*** This regiment subsequently became the 6th Regiment Mississippi Cavalry, and Capt. Lipscomb's Company was also known as Company K, of that organization

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Robert Miller, Private, Capt. Thos. Coopwood's Company, (Monroe Rangers),**** enlisted September 5, 1861 at Aberdeen, Miss., enrolled September 23, 1861 at Jackson by Wm. F. Down and mustered into service September 25 at Marion, Miss. for the war, recorded absent without leave October 31, 1862, recorded at the end of the year, 1862 as killed in Monroe County in an affray, no further records

**** This company subsequently became Company L, 24th Regiment Mississippi Infantry

M269: Compiled Service Records of Confederate Soldiers Who Served in Organizations from the State of Mississippi