Elsweyr
The Horsemen rode to Elsweyr, riding through evening and night until they reached the province. Across the border they rode, stopping for nothing and tirelessly charging forwards... Although tireless would hardly be the word to describe their now overused steeds, transforming them to beasts of burden carrying their masters across the Empire. 
No horse should have to endure such a dash, and by the time they reached Orcest their horses were at the breaking point and it was already into the early morning, 7:00 AM. The horsemen came to a halt here, the four of them tending to their steeds and taking a few moments to eat and drink, as the road ahead was hardly the most hospitable. They set off again at 9:00, working the horses who had been given so little time to recover into the ground again
They caught up to the convoy at 10:00 and lingered behind as they rode after it, waiting to pounce the bandits should they come to sight and deliver a quick strike to the bandits hearts. They had no doubt they could take on a ragtag group of bandits, and hopefully the bandits would mistake them as a larger force than they really were in the heat of battle and retreat

Imperial Legion Garrison, Fort Istirus
The Long Resurected fort had been reoccupied for the Legion years ago, designed to watch the river that ran between Valenwood and Cyrodiil. The Imperial Legion Garrison there had been awaiting the return of their messenger from Valenwood, and indeed he arrived in the small rowboat he had used to cross it and delivered the message directly to Legate Brutus
"What did they saw Anglor?" The Legate asked as he emerged with his Body Guards, and the Bosmer struck a salute
"Legate Brutus, sir, Valenwood will rise up against the Thalmor, they await our forces invasion as their signal" The Wood elf reported
"Excellent work, Anglor, another province for the Empire!" The Legate chuckled, clapping his hands together
"Uh... Well, actually Legate Brutus, Sir... They aren't going to join the Empire..." The Bosmer said sheepishly, and the Legate gave a sigh of disbelief
"Truely?" The Legates voice carried no small amount of disappointment "By the Nine, tell me you at least secured Military Access?"
"I did, sir, but our forces are restricted from damaging the tree's."
"I see Anglor, Dismissed" The Legate sighed weakly, turning and examining the shoreline, plotting his next move

A Summit In the North (High Rock)

As there were the different factions in High Rock and no single over all ruler, multiple messengers rode to each of the four kingdoms and the one republic, carrying variations of a similar letter which they delivered to the guard upon arrival
"A message from the Emperor!" They would declare "He calls a Summit."
[i](Ruler Title and Name)
I request your presence at a Summit regarding the threat of the Aldmeri Dominion to the races of men and the free peoples of Tamriel, to be held on the Isle of Balfiera, in the Iliac Bay, near the borders with both Skyrim and Hammerfell. With some fortune, the Summit will be attended by both Vanquisher Temijen of Hammerfell and The Dovahkiin, High King Giles of Skyrim.
Emperor Gaius Triarius the First [/i]

A Summit in the North (Hammerfell)
The Imperial Rider rode through the heat of Hammerfell to the gates of Sentinel. He knew of this land only what the maps had told him, and he had followed their instructions to Sentinel. He called out to the Redguards
"Hail, noble redguards! I carry a message from beyond your southern border, from Emperor Triarius!" The Rider called, taking the note and delivering it with a small smile upon his face
[i]Vanquisher Temijen
I humbly request your presence at a Summit regarding the threat of the Aldmeri Dominion to all the races of man and the free peoples of Tamriel, to be held on the Isle of Balfiera, in the Iliac Bay, near the borders with both Skyrim and Hammerfell. With some fortune, the Summit will be attended by both the Breton lords of High Rock and The Dovahkiin, High King Giles of Skyrim.
Emperor Gaius Triarius the First [/i]

A Summit in the North (Skyrim) ((I am going to assume that since Ulfric is the only Jarl as being mentioned to die, Giles became High King ruling from Windhelm))
The Imperial Rider endured the bitter cold of Skyrim as he rode for Windhelm. He knew Skyrim well, he had lived here before and served in the legion during the Civil War... The outcome of which still embittered him to this day, more than any frost could do
"Hail, our nordic brothers! I carry a message from Emperor Triarius of Cyrodiil!" The Rider called, taking the note and delivering it with a small smile upon his face
[i]The Dragonborn High King Giles
I humbly request your presence at a Summit regarding the threat of the Aldmeri Dominion to all the races of man and the free peoples of Tamriel, to be held on the Isle of Balfiera, in the Iliac Bay. With some fortune, the Summit will be attended by both the Breton lords of High Rock and Vanquisher Temijen of Hammerfell
Emperor Gaius Triarius the First [/i]