An engine block is the main casting of an internal combustion engine. The block is where the pistons, crankshaft, and typically the camshaft ride.
After the rough casting is made the crank bore is cut through the long axis of the block to provide a true line through the bearing saddles. Once the crank line is cut the piston cylinders are bored out at a 90 degree angle to the crank line. The camshaft bore is then cut parallel to the crank line. The top of the block called the deck is machined flat to receive the engine head. Finally the mating surfaces for the oilpan, timing cover, bellhousing, etc. are cut.In the early days of automotive production engine blocks were two piece castings, the crank section being manufactured separately from the piston bore and the two, or three in the case of V engines, pieces being bolted together. One piece blocks were hard to engineer and expensive to produce. It wasn't until the development of the Ford flathead engine in 1931 that monolithic cast blocks came into mainstream use. | 
