This is a photograph from the National Archive collection in London contains images of preparations for the battle of Magdala. This is a summary of the Wikimedia story about this extraordinary campaign. You can see more here.
Martin
The Battle of Magdala was fought in April 1868 between British and Abyssinian forces at Magdala, 390 miles (630 km) from the Red Sea coast, which at that time was the capital city of Abyssinia (now known as Ethiopia). The British were led by Robert Napier, while the Abyssinians were led by Emperor Tewodros II.
In March 1866 a British envoy had been dispatched to secure the release of a group of missionaries who had first been seized when a letter Tewodros II had sent to Queen Victoria requesting munitions and military experts from the British, delivered by an envoy, Captain Cameron, had gone unanswered. They were released; however Tewodros II changed his mind and sent a force after them and they were returned to the fortress and imprisoned again, along with Captain Cameron.
The British won the battle, and Tewodros committed suicide as the fortress was finally seized.
Martin Plaut 
Thanks for sharing!
Is this perhaps the earliest photograph of Eritrea ?