Place olive oil in heavy skillet; add garlic, onion, celery and parsley.
Fry until onion is golden brown.
Add tomato paste and thin with juice of tomato; bring to simmer point.
Add tomatoes, a little at a time, to keep sauce at the simmer point.
When all tomatoes have been added, pour in 1 quart water.
Cover; simmer for 1 hour and 30 minutes.
If mixture cooks down, add more water and reduce heat.
Add seasonings to sauce and simmer 30 minutes longer.
Kill crab by inserting knife behind the head and pry back shell up.
Separate legs from body and clean thoroughly by scrubbing with a stiff brush.
Discard back shell and stomach waste.
Crack leg shells; break up body into six or eight chunks.
Set aside.
Scrub clam shells well; rinse prawns.
Transfer sauce to large cooking kettle; remove garlic if desired.
Place crab, clams and prawns in sauce; cover and cook on low heat until done 30 to 45 minutes or until clam shells pop open.
Serve with French bread.