State transportation officials on Tuesday will present the City Council with a new design for reconstruction of the Cradock Bridge in Medford Square. The historic bridge, which carries Main Street over the Mystic River, features stone arches. It is a key entry point to downtown. The original bridge on the site was built in 1637. The projected, estimated to cost $10 million to $12.7 million and to be funded entirely by the state, is expected to start in the spring of 2014. A temporary bridge adjacent to the Cradock Bridge, with two lanes in each direction, will be constructed to ease traffic flow while the old bridge is rebuilt. The council meets at 6 p.m. in City Hall.