calmly isolated from the action is enrico scrovegni, who paid for all this art in an attempt to gain forgiveness for the sins of his wealthy and greedy father. these frescoes are considered by many to be a precursor of the renaissance to come. with this masterpiece, created 200 years before leonardo and michelangelo, giotto seems to be making it clear -- europe was breaking out of the middle ages. >> narrator: tonight on frontlinin yemen, rival militants are fighting for control of the country-- al qaeda in the arabian peninsula, and now the houthis, with their hostile message to america and its allies: >> narrator: journalist safa al ahmad spent months reporting from the middle of the conflict. >> narrator: she negotiated rare access to the houthi rebels as they advanced. >> narrator: and she traveled into the heartland of al qaeda

calmly isolated from the action is enrico scrovegni, who paid for all this art in an attempt to gain forgiveness for the sins of his wealthy and greedy father. these frescoes are considered by many to be a precursor of the renaissance to come. with this masterpiece, created 200 years before leonardo and michelangelo, giotto seems to be making it clear -- europe was breaking out of the middle ages. [train whistle toots] [bouncy music] - [singing] ♪ they're two, they're four ♪ they're six, they're eight ♪ shunting trucks and hauling freight ♪ ♪ red and green and brown and blue ♪ ♪ they're the really useful crew ♪ ♪ all with different roles to play ♪ ♪ round tidmouth sheds or far away ♪ ♪ down the hills and round the bends ♪ ♪ thomas and his friends male narrator: thomas & friends is made possible in part by: all-inclusive experience is a proud sponsor of thomas & friends. providing families a place to play, share, and learn through kid clubs found at hard rock hotel cancun, punta cana, and riviera maya. male narrator: and by contributions to your pbs station from viewers like you.