Built in 1574, the Iglesia Santa Bárbara (Calle Isabel La Católica and Gabino Puello, 8:30 a.m.–7 p.m. daily, free) was constructed in honor of the patron saint of the military, so it’s a little bit church and a little bit fortress.
The white-washed, baroque structure is an amalgamation of pieces due to, yet again, the sacking that Drake gave it. The rebuilt church was put together like jammed puzzle pieces with three arches, two of which are windowless. Still, these additions are probably what kept it from toppling during some hefty hurricanes through the ages.
Just behind the church is the Fuerte de Santa Bárbara (Juan Parra at Av. Mella), which was erected in 1570 as a security defense for the city (and to keep the Taíno slaves in check). All that was to no avail when Drake blew through Samto Domingo [1]. He easily captured it in 1586, and the rubble goes to show how quickly it went down.
Links:
[1] http://www.moon.com/destinations/dominican-republic/santo-domingo