How did Ethiopia defeat Italy at the battle of adwa?

The Ethiopians surrounded the Italians for two weeks and, upon Empress Tayitu's advice, cut off the fort's water supply. The Italian commander agreed to surrender if they would be allowed to leave with their firearms. Menelik agreed that they could leave the garrison unharmed.

Explanation:

The Italians in the end, signed the Treaty of Wuchale with Menelik in May 1889. The treaty was written in Amharic and Italian. It would later be the trigger for the battle of Adwa. It was effectively made Ethiopia Italy's protect, difference to the Amharic version.