In the aftermath of the revolution in Ukraine - in which pro-Western and nationalist Ukrainians have taken power after the fall of pro-Russia President Viktor Yanukovych - there are fears that the southern region of Crimea could become a battleground between forces loyal to Ukraine and Russia. Here are five things you need to know about Crimea.
1. Popular holiday destination
Crimea, a rugged strategic peninsula jutting into the Black Sea, has been a popular vacation spot for Ukrainians and Russians since the time of the tsars. Its balmy climate, vineyards, orchards and the "green riviera" along its southern coast make for some stunning scenery.
It is a centre of pro-Russian sentiment, which can spill into separatism. The region has 2.3 million inhabitants, most of whom identify themselves as ethnic Russians and speak Russian. The region voted heavily for Viktor Yanukovych in the 2010 presidential election, and many people there believe he is the victim of a coup - leading to attempts by separatists in Crimea's parliament to push for a vote on whether it should leave Ukraine.
2. Historically Russian-ruled
Russia has been the dominant power in Crimea for most of the past 200 years, since it annexed the region in 1783. However, it was transferred by Moscow to Ukraine - then part of the Soviet Union - in 1954. Some ethnic Russians see that as a historical wrong.
However, another significant minority, the Muslim Crimean Tatars, point out that they were once the majority in Ukraine, and were deported in large numbers by Soviet leader Joseph Stalin in 1944 for alleged collaboration with Nazi invaders in World War II.
Ethnic Ukrainians made up 24 per cent of the population in Crimea according to the 2001 census, compared with 58 per cent Russians and 12 per cent Tatars.
Tatars have been returning since the collapse of the Soviet Union in 1991 - causing persistent tensions with Russians over land rights.0
3. Legal status
Crimea remains legally part of Ukraine - a status that Russia backed when pledging to uphold the territorial integrity of Ukraine in a memorandum signed in 1994, also signed by the US, UK and France.
It is an autonomous republic within Ukraine, electing its own parliament. However, the post of Crimean president was abolished in 1995, shortly after a pro-Russian Crimean separatist won the post with a big majority. It now has a presidential representative, and a prime minister, but both are appointed by Kiev.
4. Russia's presence
Russia keeps a major naval base in the Crimean city of Sevastopol, where its Black Sea Fleet is based. Some Ukrainians are therefore nervous about Russia's military might being brought to bear.
The lease stipulates that Russian personnel should not take military equipment or vehicles outside the base area without Ukrainian permission. Mr Olexander Turchynov, Ukraine's acting president, warned that any move by Russian troops off of their base in Crimea "will be considered a military aggression".
There are reports of Russian envoys distributing Russian passports in the peninsula. Russia's defence laws allow military action overseas to "protect Russian citizens". This has sparked fears of Russia using this as a pretext for invasion.
5. Florence Nightingale
Crimea has seen many wars in its history. The most famous is the Crimean War of 1853-1856, in which Britain and France defended the Ottomans against Russia. The legendary Florence Nightingale was sent to nurse wounded British soldiers in that war.
Source: BBC, AFP, REUTERS