These additional events apply for the Building phase of the round. There are 6 events during which the buildings below cannot be constructed:
1) Wheat Silo. 2) Road. 3) Bridge. 4) Temple. 5) Palace. 6) Fortifications.
The additional events are considered different from the solo cards, so at any given round in a solo game, up to 2 different buildings may not be constructed. If a building is already built, the event does not apply.
—description from the designer