The sprawling headquarters of the Coalition Provisional Administration, sitting on the west bank of the Tigris, escaped from Tuesday night's attack unscathed. There are some signs that security in central Baghdad has been stepped up. Late on Tuesday night, a military checkpoint appeared on one of the main roads in the city's business and commercial district. On Wednesday morning, a higher profile US army presence was on the streets outside the fortified hotels where most foreigners stay. But there's a limit to what the occupying powers can do. To close down Baghdad with endless checkpoints and a large number of troops on the streets would not only provide attackers with a greater range of softer targets, it would also make the city feel yet more occupied. Better intelligence, rather than a heavy-handed security presence, is what the coalition needs most.