Syria: The military, the militias and the spies
When it comes to the forces of the Syrian government there is an extraordinarily complex and opaque relationship between the military, the militias, the numerous intelligence agencies and the various power centres that control them.
This is one of the reasons why apportioning individual blame for massacres like the one that took place at Houla last Friday is so difficult and why Syria's President Bashar al-Assad has been able to keep a straight face while denying any culpability for recent atrocities.
The various forces are:
Syria has a large, powerful, but far from invincible military, equipped with weaponry supplied mainly by Russia and recently Iran.
When a civilian area - like Baba Amr in Homs - is shelled it is most likely to be by the conventional Syrian army, acting on orders stemming from a military chain of command.
Brig General Hashem, a former Syrian soldier, says unmanned aerial drones supplied by Iran since the uprising began 15 months ago are being used extensively to guide artillery units onto which buildings to target and flatten.
"These drones were unheard of in Syria until Iran started supplying them," he says.
Russia has also reportedly been shipping very large quantities of arms to its long-standing ally Syria, including thousands of sniping rifles used by government forces positioned on rooftops to pick off activists in the street.
Syria, like almost any country, has an army, a navy and an airforce. It has a conscript army with 18 months compulsory service, backed by about 200,000 regular soldiers, two thirds of whom are said to be from the same Alawite minority sect as the president and his regime.
Syria's sizable military is no match for Israel's - it was beaten in both the 1967 and 1973 wars - and it stayed out of the 2006 Lebanon War.
Since the current uprising began last year Syrian armour, notably the 4th Mechanised Division, has been used extensively to crush internal opposition. Tanks and armoured personnel carriers have become a frequent sight in areas of protest or opposition.
Withdrawing this heavy weaponry to barracks is one of the demands of Kofi Annan's UN-backed ceasefire plan. But since it has not happened, the rebels are trying hard to acquire the sort of modern anti-tank weapons that wreaked such damage on Israel's Merkava tanks in southern Lebanon in 2006.
With Russian help, Syria has an extensive air defence network that could make enforcing any future no-fly zone difficult, if one was ever implemented.
When Israeli warplanes destroyed a suspected Syrian nuclear site in 2007 they were able to evade the air defences by electronic jamming. Since then, Syria's air defences have been reviewed and it is far from certain that such an operation could be repeated.
The Intelligence Agencies
Syria has a sprawling network of 17 intelligence agencies that fall into four broad categories, all aimed primarily at maintaining the regime in power.
Military Intelligence, known as al-Mukhabarat, is under control of the president and focuses on monitoring dissidents.
Airforce intelligence is one of the most deeply established and all-pervasive branches of state security. It was responsible for trying (unsuccessfully) to smuggle a bomb on board an Israeli airliner out of Heathrow in 1986.
The General Security Directorate comes under the Ministry of Interior, while the Political Security Directorate is perhaps the most vigorous of all in pursuing the regime's opponents inside the country.
Just like in Egypt under President Mubarak, the numbers of people working in Syrian intelligence are vast - one former insider puts it at least 150,000.
And like in Ceaucescu's Romania or Communist East Germany, informants are everywhere, reporting back - for a small reward - unguarded comments deemed critical of the president or his regime. Such comments, even if invented, can lead to months of torture in detention centres, sometimes ending in death.
The detention centres are distributed throughout the country and some of the abuses carried out in them are well documented by human rights organisations. Amnesty International, in its 2012 report, quotes graphic examples of torture carried out by Military Intelligence, State Security, Political Security and Airforce Intelligence.
Known as shabiha, these are the blunt edge of Syrian state repression and undoubtedly responsible for some of the worst atrocities yet committed.
Essentially they are street thugs, often with criminal backgrounds, and some with connections to smuggling mafias along the coast.
With no official status and no uniform - other than their favoured black leather jackets - they are guns for hire, swarming into certain districts when ordered to, usually on a Friday, a day that has become the traditional day of protest across the Arab world.
The shabiha operate at very much a local level, making it hard to trace their crimes back to anyone high up in government in Damascus. Many, but not all, are from the president's Alawite clan but their loyalty appears to be to whoever is paying them rather than to any ethnicity or religion.
They are the perpetrators of the proverbial "dirty deeds done dirt cheap". In the case of the Houla massacre it is quite possible that following the artillery bombardment they were sent in by someone locally to "finish the job", slitting the throats of survivors or shooting them in the head.
Local sources say they may well have been hired to carry out an act of vengeance against Sunni villagers after rebels from the Free Syrian Army shelled nearby Alawite villages with captured mortars.
The shabiha do not appear in any official command structure but analysts say they are "a useful tool for the government to carry out repression at arm's length".
The Syrian government continues to deny it is responsible for repression or torture.