Civil War mortors

[PWC]

Why wsre the "tubes" on the mortors so much thicker than the cannons a t parrot "rifles"?

[dryheat]

I've never looked into it, but always wondered about the elephant sized "barrels".

[Fred Pillot]

Probably to create WEIGHT. To lob an explosive shell over a wall does not need length but still needs resistance.

[Merc]

The size of the mortar tube was dictated by the size of the explosive shell it fired and size of the powder charge that yielded the desired distance.

A short range 10 inch siege mortar shell could weigh up to 88 pounds requiring the siege mortar tube to weigh 1852 pounds to fire a shell several hundred yards.

A long range 13 inch seacoast mortar shell could weigh up to 197 pounds, but the heavy powder charge needed to fire the shell a much longer distance required the seacoast mortar tube to weigh an astounding 17,120 pounds.

[Clark Howard]

The black powder employed in these mortars is classed as an explosive. The thick barrels were required to contain that explosive impulse. Later, smokeless powders, are classed as propellants, which deliver a much longer, more manageable impulse.

[Sunray]

Parrot "rifles" were the first 'modern' artillery. Used a case and was a breech loader.
An early mortar fired a much bigger projectile and did not have a carriage to help absorb the recoil. 'Bigger' means it needs more powder. That meant it had to have thick barrels walls like Clint says.
The U.S. Army in the 1860's had a 13" mortar. In 1646, the English had a 15.5" mortar that fired a 220 pound shell(big hollow ball filled with BP). During the Siege of Rhodes in 1480 the Knights Hospitaller(as in The Knights of St. John who teach first aid now) had a mortar that fired a 260 kg(about 572 lbs) granite stone(literally chiseled round) to 100 to 200 yards. The gun weighs(it's currently in a Paris museum) 3,325 kg(7315 lbs).