Monte Mario (Rome) Italy 1 (deprecated, 3.6, use 3003, Greenwich) - EPSG:26591

WKT

PROJCS["Monte_Mario_Rome_Italy_1", 
	GEOGCS["GCS_Monte_Mario_Rome", 
		DATUM["D_Monte_Mario", 
			SPHEROID["International_1924", 6378388.0, 297.0]], 
		PRIMEM["Rome", 12.45233333333333], 
		UNIT["Degree", 0.0174532925199433]], 
	PROJECTION["Transverse_Mercator"], 
	PARAMETER["False_Easting", 1500000.0], 
	PARAMETER["False_Northing", 0.0], 
	PARAMETER["Central_Meridian", -3.45233333], 
	PARAMETER["Scale_Factor", 0.9996], 
	PARAMETER["Latitude_Of_Origin", 0.0], 
	UNIT["Meter", 1.0]]

WKT2

PROJCRS["Monte_Mario_Rome_Italy_1", 
	BASEGEOGCRS["GCS_Monte_Mario_Rome", 
		DATUM["D_Monte_Mario", 
			ELLIPSOID["International_1924", 6378388.0, 297.0]], 
		PRIMEM["Rome", 12.45233333333333, 
			ANGLEUNIT["Degree", 0.0174532925199433]], 
		CS[ellipsoidal, 2], 
		AXIS["Latitude (lat)", north, 
			ORDER[1]], 
		AXIS["Longitude (lon)", east, 
			ORDER[2]], 
		ANGLEUNIT["Degree", 0.0174532925199433]], 
	CONVERSION["Transverse_Mercator", 
		METHOD["Transverse_Mercator"], 
		PARAMETER["False_Easting", 1500000.0], 
		PARAMETER["False_Northing", 0.0], 
		PARAMETER["Central_Meridian", -3.45233333], 
		PARAMETER["Scale_Factor", 0.9996], 
		PARAMETER["Latitude_Of_Origin", 0.0]], 
	CS[Cartesian, 2], 
	AXIS["Easting (X)", east, 
		ORDER[1]], 
	AXIS["Northing (Y)", north, 
		ORDER[2]], 
	LENGTHUNIT["Meter", 1.0], 
	ID["EPSG", "26591"]]

Data from @esri/proj-codes

{
  "wkid": 26591,
  "latestWkid": 26591,
  "gcsWkid": 4806,
  "macro": "PE_PCS_MONTE_MARIO_ROME_ITALY_1",
  "name": "Monte_Mario_Rome_Italy_1",
  "wkt": "PROJCS[\"Monte_Mario_Rome_Italy_1\",GEOGCS[\"GCS_Monte_Mario_Rome\",DATUM[\"D_Monte_Mario\",SPHEROID[\"International_1924\",6378388.0,297.0]],PRIMEM[\"Rome\",12.45233333333333],UNIT[\"Degree\",0.0174532925199433]],PROJECTION[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",1500000.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",-3.45233333],PARAMETER[\"Scale_Factor\",0.9996],PARAMETER[\"Latitude_Of_Origin\",0.0],UNIT[\"Meter\",1.0]]",
  "wkt2": "PROJCRS[\"Monte_Mario_Rome_Italy_1\",BASEGEOGCRS[\"GCS_Monte_Mario_Rome\",DATUM[\"D_Monte_Mario\",ELLIPSOID[\"International_1924\",6378388.0,297.0]],PRIMEM[\"Rome\",12.45233333333333,ANGLEUNIT[\"Degree\",0.0174532925199433]],CS[ellipsoidal,2],AXIS[\"Latitude (lat)\",north,ORDER[1]],AXIS[\"Longitude (lon)\",east,ORDER[2]],ANGLEUNIT[\"Degree\",0.0174532925199433]],CONVERSION[\"Transverse_Mercator\",METHOD[\"Transverse_Mercator\"],PARAMETER[\"False_Easting\",1500000.0],PARAMETER[\"False_Northing\",0.0],PARAMETER[\"Central_Meridian\",-3.45233333],PARAMETER[\"Scale_Factor\",0.9996],PARAMETER[\"Latitude_Of_Origin\",0.0]],CS[Cartesian,2],AXIS[\"Easting (X)\",east,ORDER[1]],AXIS[\"Northing (Y)\",north,ORDER[2]],LENGTHUNIT[\"Meter\",1.0],ID[\"EPSG\",\"26591\"]]",
  "description": "Monte Mario (Rome) Italy 1 (deprecated, 3.6, use 3003, Greenwich)",
  "authority": "EPSG",
  "version": "2.1(3.0.1)",
  "deprecated": "yes",
  "areaname": "Italy - west of 12~E",
  "extent": {
    "slat": 36.53,
    "nlat": 47.04,
    "llon": 5.93,
    "rlon": 12
  }
}