Ancient empires frequently reinforced their borders by building churches along them. Latvia is a country that has seen many lords and cultures come and go - German, Russian, Polish and Swedish to name a few. Riga reflects these cultures with many beautiful examples of Religious architecture.
The examples used on the book cover are, from left to right:
Riga St. Francis Roman Catholic church (basilica) was built from 1889-1892. The towers are a combination of Neo-Gothic and Neo-Romanesque.
The Muslim religion is very sparse in Latvia. The image that was used to represent a Mosque is a building on Maskavas iela.
The Orthodox church is The Grebenschikov Prayer House of Old-Believers. Building Began in 1814 and was completed, in it's present form, in 1906.
The last church is St. Paul's Evangelical Lutheran Church. This is a Neo-Gothic church built in 1885-1887.