Russian to English Tech/Engineering Architecture Courtyard gate construction

Still in the same old Tashkent courtyard as in my last question, only now we're exiting the courtyard into an alleyway.

"Бряцая ключами, дедушка отпер старые деревянные ворота. Перешагнув через нижнюю перекладину, он махнул мне рукой и, шаркая сапогами, зашагал по переулку."

Draft: "Rattling his keys, Grandfather unlocked the old wooden gate. He lifted his boots to step across the lower ???, waved to me and shuffled off down the alley."

What is the перекладина, across which the old man stepped from the courtyard into the alley? I can't picture it's being the lower rail of the gate. But if it's somehow the threshold or sill, then why "lower"? I may have to put it on a list to ask the author, but maybe somebody here has been in such houses.

(Please ignore the fact that I moved the boots from the "shuffling" to the "stepping"; it may be necessary to move them back, but that's not the question at the moment.)