In our world, before the invention of radio the only ways to communicate during a battle were by sound or sight over long distances or by in-person messages.
- Trumpets (or horns or bugles) can be heard over great distances. Different tunes and rhythms can be used to convey orders such as advance or retreat. Drums can be used in the same way over shorter distances.
- Flags are flown on buildings and ships to indicate which group controls them.
- Flags that accompany a leader tell troops where they should be and help to identify enemies.
- Commanders who are not in the same place can communicate by sending a written or verbal message through a messenger on horseback.
Many of these methods were used in the Battle of the Pelennor Fields.
When the Rohirrim arrive at the northern wall, the whole of the Pelennor is occupied by Sauron's army and the sky is dark. Théoden's battle plan is, of necessity, simple.
‘Éomer, my son! You lead the first éored,’ said Théoden; ‘and it shall go behind the king’s banner in the centre. Elfhelm, lead your company to the right when we pass the wall. And Grimbold shall lead his towards the left. Let the other companies behind follow these three that lead, as they have chance. Strike wherever the enemy gathers. Other plans we cannot make, for we know not yet how things stand upon the field. Forth now, and fear no darkness!’
The Lord of the Rings Book Five, Chapter 5: The Ride of the Rohirrim
Page 836 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)
After learning that the wind is beginning to blow the dark clouds away, Théoden issues his stirring call to arms and sounds a horn for the charge. This communicates the presence of the Rohirrim to the army of Gondor.
With that he seized a great horn from Guthláf his banner-bearer, and he blew such a blast upon it that it burst asunder. And straightway all the horns in the host were lifted up in music, and the blowing of the horns of Rohan in that hour was like a storm upon the plain and a thunder in the mountains.
The Lord of the Rings Book Five, Chapter 5: The Ride of the Rohirrim
Page 838 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)
The charge of the Rohirrim clears Sauron's army from the northern part of the Pelennor and allows the army of Gondor to push out of the now destroyed gates of Minas Tirith. After Théoden is killed, Éomer leads his men further south while the King's men carry Théoden's body and Éowyn towards the gates of the city. On the way to the gates, they meet Imrahil leading the army of Gondor into battle. This is the first record of dialog between the two armies during the battle and Imrahil learns that Théoden is dead and that Éomer now leads the Rohirrim.
It was through a mist that presently he saw the van of the men of Gondor approaching. Imrahil, Prince of Dol Amroth, rode up and drew rein before them.
‘What burden do you bear, Men of Rohan?’ he cried. ‘Théoden King,’ they answered. ‘He is dead. But Éomer King now rides in the battle: he with the white crest in the wind.’
The Lord of the Rings Book Five, Chapter 6: The Battle of the Pelennor Fields
Page 845 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)
As the battle wears on and begins to turn in Sauron's favour, Aragorn approaches the Harlond on the ships of the Corsairs. People in Minas Tirth attempt to use bells and trumpets to recall their army (thinking that the ships are reinforcements for Sauron). This attempt at communication is unsuccessful.
‘The Corsairs of Umbar!’ men shouted. ‘The Corsairs of Umbar! Look! The Corsairs of Umbar are coming! So Belfalas is taken, and the Ethir, and Lebennin is gone. The Corsairs are upon us! It is the last stroke of doom!’ And some without order, for none could be found to command them in the City, ran to the bells and tolled the alarm; and some blew the trumpets sounding the retreat. ‘Back to the walls!’ they cried. ‘Back to the walls! Come back to the City before all are over- whelmed!’ But the wind that sped the ships blew all their clamour away.
The Lord of the Rings Book Five, Chapter 6: The Battle of the Pelennor Fields
Page 846-7 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)
Éomer believes the battle is lost and prepares for a last stand until Aragorn communicates his arrival by displaying the royal standard of Gondor that Arwen had sent him.
And then wonder took him, and a great joy; and he cast his sword up in the sunlight and sang as he caught it. And all eyes followed his gaze, and behold! upon the foremost ship a great standard broke, and the wind displayed it as she turned towards the Harlond. There flowered a White Tree, and that was for Gondor; but Seven Stars were about it, and a high crown above it, the signs of Elendil that no lord had borne for years beyond count. And the stars flamed in the sunlight, for they were wrought of gems by Arwen daughter of Elrond; and the crown was bright in the morning, for it was wrought of mithril and gold.
The Lord of the Rings Book Five, Chapter 6: The Battle of the Pelennor Fields
Page 847 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)
Aragorn meets Éomer in the thick of the battle and they talk.
And so at length Éomer and Aragorn met in the midst of the battle, and they leaned on their swords and looked on one another and were glad. ‘Thus we meet again, though all the hosts of Mordor lay between us,’ said Aragorn. ‘Did I not say so at the Hornburg?’ ‘So you spoke,’ said Éomer, ‘but hope oft deceives, and I knew not then that you were a man foresighted. Yet twice blessed is help unlooked for, and never was a meeting of friends more joyful.’ And they clasped hand in hand. ‘Nor indeed more timely,’ said Éomer. ‘You come none too soon, my friend. Much loss and sorrow has befallen us.’ ‘Then let us avenge it, ere we speak of it!’ said Aragorn, and they rode back to battle together.
The Lord of the Rings Book Five, Chapter 6: The Battle of the Pelennor Fields
Page 848 (Houghton Mifflin Harcourt; Single Volume 50th Anniversary Edition)
