More than 140,000 men were killed on the two sides. Over 85,000 of that figure were from the Ottoman side.
Fighting against the Turkish defenders were the British Army, soldiers from Commonwealth countries (i.e. Australia, New Zealand and India) and France. See the images further below.
Soldiers from Australia and New Zealand (ANZACS) played a leading role.
After fighting for eight months in what could be described as a stalemate the allies evacuated the peninsula.
Friday marked the start of commemorations for those who died during the campaign. Thousands (mainly Australians and New Zealanders) are expected to attend commemorative events on the peninsula on Saturday.
To see what Gallipoli was like a hundred years ago see the images below.
What keeps the world ticking? James is always looking for the answer and the latest news from around the globe. When he's not behind his computer, he's basking in the Thailand sun, or dreaming of the southern hemisphere, where he grew up in rural Australia.